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This paper explores the theory of freedom that Emilie du Châtelet advances in her essay "On Freedom." Using contemporary terminology, we can characterize this theory as a version of agent-causal compatibilism. More specifically, the theory has the following elements: (a) freedom consists in the power to act in accordance with one's choices, (b) freedom requires the ability to suspend desires and master passions, (c) freedom requires a power of self-motion in the agent, and (d) freedom is compatible with moral necessity but not with physical necessity. While these elements may at first appear disparate, the paper shows that they fit together quite well. The resulting theory is a surprising combination of doctrines that appear to be based on Samuel Clarke's libertarian account of free will and doctrines that are reminiscent of the compatibilist accounts of John Locke, Anthony Collins, Gottfried Leibniz, and Thomas Hobbes.


Du Châtelet, freedom, liberty, compatibilism, self-motion, occasional causation, moral necessity, Samuel Clarke, Voltaire

in 1737, voltaire sent a short piece titled "On Freedom" to Frederick of Prussia, claiming that it was his own work.1 The 19-page-long essay puts forward an intriguing theory of freedom. It discusses, among other things, the compatibility of divine foreknowledge with human freedom, the determination of actions by the agents' perceptions of the good, the relation between will and judgment, the difference between divine and human freedom, and the difference between the freedom of adults and that of children. Because "On Freedom" overlaps in certain ways with chapter VII of Voltaire's 1734 Treatise of Metaphysics, scholars used to treat it as a revision of, or companion piece to, that chapter.

Yet, historians have now uncovered compelling evidence that "On Freedom" was written not by Voltaire but by Emilie du Châtelet, during the time that she spent with Voltaire at Cirey.2 It appears that she intended to include the piece in her [End Page 255] Foundations of Physics, though, in the end, she did not publish it.3 It is not entirely clear why Voltaire sent it to Frederick under his name; perhaps it was simply a ruse. In any case, the piece's similarities to Voltaire's Treatise of Metaphysics, and even some verbatim overlaps, should not be surprising. After all, Du Châtelet was working through the Treatise with Voltaire at the time—he had, in fact, composed it for her—and even helped him revise it.4 Hence, it makes sense for Du Châtelet to base her piece on Voltaire's chapter. Moreover, there are many significant differences between the discussions of freedom in the Treatise and in "On Freedom."5 In fact, the aspects of "On Freedom" on which I focus in this paper and that I find most interesting do not seem to be based on Voltaire's work.

Scholars of early modern philosophy have not paid much attention to "On Freedom" so far,6 even though it presents a rich theory of freedom and is Du Châtelet's most thorough discussion of the topic. My paper aims to provide an interpretation of this theory. I argue that Du Châtelet is best understood, in present-day terminology, as a proponent of a form of agent-causal compatibilism. In other words, she holds that freedom is compatible with necessitation and that each free action is caused directly by the agent, who thereby starts a new causal chain. Arguing for this requires paying careful attention to several important facets of her theory, in particular her account of self-motion and moral necessity. At first glance, these two facets may appear to suggest that Du Châtelet endorses an incompatibilist theory of freedom, that is, a theory according to which freedom requires the lack of determination or necessitation. Yet, I show that this initial impression is mistaken. The correct way to understand her account of freedom is as an agent-causal compatibilist theory.

This apparent tension between the different facets of Du Châtelet's theory points to one of the particularly surprising things about her theory: it combines elements that appear to be based on Samuel Clarke's libertarian account of free will7 with elements that are reminiscent of the compatibilist accounts of John Locke, Anthony Collins, Gottfried Leibniz, Thomas Hobbes, and others. On my interpretation, Du Châtelet endorses versions of Clarke's account of self-motion, occasional causation, and moral necessity while rejecting Clarke's claim that [End Page 256] freedom requires a lack of determination.8 If my interpretation is correct, her theory contains items that are important desiderata for libertarians like Clarke without requiring that free actions are undetermined. In particular, as already mentioned, Du Châtelet holds that agents start new causal chains when acting freely; free actions are not efficiently caused by any prior event.

Admittedly, the term 'compatibilism' is anachronistic. Yet, the concept is not: in Du Châtelet's time, the question of whether free actions can be determined or necessitated was central to discussions of freedom, and there was widespread disagreement about it.9 For the sake of brevity, I will use the term 'compatibilism' to describe theories according to which free actions can be determined or necessitated, and 'incompatibilist' to describe theories according to which free actions cannot be determined or necessitated. One thing that is important to keep in mind in this context, and that I will discuss at length in section 4, is that 'determine' and 'necessitate' can mean a number of different things. For instance, like some other early modern philosophers, Du Châtelet distinguishes between physical and moral necessity. Hence, the term 'compatibilism' does not tell us what type of determination or necessity is compatible with freedom; we will need to discuss that question separately. Labeling Du Châtelet's theory 'compatibilist' merely means that it views freedom as compatible with some type of necessity or determination.

The structure of this paper is as follows. In section 1, I present textual evidence that Du Châtelet puts forward a compatibilist theory of freedom, that is, that she takes freedom to be compatible with determination. In fact, I show that a superficial reading of "On Freedom" may suggest that she embraces a compatibilism similar to Thomas Hobbes's. Next, in section 2, I explore one of the ways in which Du Châtelet's theory is more sophisticated than Hobbes's: she stresses the importance of our ability to suspend our desires and to control our passions. In section 3, I then turn to Du Châtelet's account of self-motion, or agent causation, and its role in free actions. To me, this is the most fascinating aspect of her theory. While Du Châtelet's account of self-motion may initially seem to undermine her commitment to compatibilism, I will argue that this impression is mistaken and that these two commitments of the theory harmonize quite well. Section 4 explores a final facet of Du Châtelet's account of freedom, namely, her insistence that free actions are only morally necessary. We will see that this aspect of the theory also fits together excellently with the other aspects; the overall theory forms a coherent whole. Finally, in section 5, I turn to two potential objections to my claim that Du Châtelet is a compatibilist. First, she struggles to reconcile human freedom with divine foreknowledge in "On Freedom," settling in the end for an appeal to divine mystery. Second, she states, in some letters from around the same time, that she does not know how to reconcile freedom with the laws of motion. Both of these sets of passages may appear to suggest that Du Châtelet [End Page 257] was an incompatibilist. Yet, I argue, a closer examination dispels both objections; in fact, these objections ultimately help us understand important aspects of Du Châtelet's agent-causal compatibilism.

1. freedom of action and compatibilism

At the surface level, Du Châtelet's theory can look like a very straightforward and traditional form of compatibilism. She writes, for example, "When one says that we are not free regarding the act of willing itself, that does nothing to our freedom, because freedom consists in acting or not acting, and not in willing and not willing" ("On Freedom," 491).10 We could not ask for a more explicit statement: she claims that the will is not free; an agent's freedom is not the freedom to will (or not will) something, but the freedom to do (or not do) something. Du Châtelet states elsewhere that this freedom is, in more precise terms, the freedom to do what one wills or wants to do: she defines freedom as "the power of thinking of one thing or of not thinking of it, of moving or not moving, in accordance with the choice of one's own mind" ("On Freedom," 485).11 Or, as she puts it later, "the true and the only freedom is the power of doing that which one chooses to do" ("On Freedom," 495).12 She points out that this is also the type of freedom that God possesses ("On Freedom," 495; 502). To quote just one more passage, she writes, "We can hardly conceive of a being that has more freedom than the capacity of doing what pleases him" ("On Freedom," 496).

The definitions we have seen so far are very similar to what is sometimes called 'simple compatibilism'—the view that whenever an agent does not encounter external obstacles in his voluntary movements and is not compelled to move by anything external, the agent is free. On this view, freedom is merely the ability to act in accordance with one's preferences or desires, or to do what one wants to do. It is not a lack of determination in willing. In other words, what matters on this view is freedom of action, not freedom of the will or of choice. Hobbes's definition of freedom is a good example of straightforward, unadulterated simple compatibilism, though there are many other early modern authors who endorse more or less straightforward versions of it.13 We will soon see that there is much [End Page 258] more to Du Châtelet's theory of freedom than this. She ends up endorsing a theory that is far more refined and powerful than simple compatibilism. Yet, it is true that the emphasis on freedom of action, and the claim that freedom does not reside in the will, is an important aspect of her theory. Hence, it is worth examining this aspect more closely before exploring the other layers of her view.

Du Châtelet's claims that freedom is the power to act in accordance with the will and that the will itself is not free are strong indications that her theory is compatibilist. After all, this strategy is central to many compatibilist theories, for instance, those of Hobbes and Locke.14 It repudiates the libertarian claim that a free agent's will cannot be determined or necessitated in its act. For proponents of this compatibilist strategy, freedom does not require the ability to will one thing or another in the same circumstances. Instead, these philosophers locate freedom in the ability to do what one has willed to do. What undermines freedom is not the determination or necessitation of the will, but obstacles—internal or external—to doing what one wants or has chosen to do. By embracing freedom of action and rejecting freedom of the will, Du Châtelet is clearly aligning herself with this tradition.

Yet, there is even more direct evidence that we should read her as a compatibilist: there are passages in which she says explicitly that freedom is compatible with at least one form of necessitation—which is all it takes to qualify as a compatibilist. For example, she says about God that "the necessity of always doing the best … destroys [God's] freedom no more than the necessity of being omnipresent, eternal, vast etc." ("On Freedom," 496). Something analogous is true for human freedom: "man is under the necessity of willing that which his judgment presents to him as best. If it were otherwise, … he would no longer be free; … being free means doing what one judges to be best" ("On Freedom," 496).15 Hence, determination or necessitation does not generally undermine freedom. In fact, the most perfectly free actions are necessitated by the agent's perceptions of the good; the last passage even states that without such necessitation, human beings would not be free. Du Châtelet appears to hold that being necessitated by the good or apparent good is desirable or a perfection.16

On the flip side, Du Châtelet explicitly rejects liberty of indifference, that is, roughly, a freedom consisting in a lack of determination by one's perceptions of the options that one is considering. Du Châtelet notes that "liberty of indifference, with respect to discernable things, is not really a kind of freedom" ("On Freedom," 493). In other words, a free agent does not need to be indifferent toward options [End Page 259] among which the agent is able to perceive differences.17 That fits with what we saw earlier: free agents can be necessitated to will what they perceive as best. If liberty of indifference were the correct account of freedom, she continues, we would have to say, absurdly, that "idiots, imbeciles, and even animals" have more freedom than we do, and that we have more freedom when we understand the options less well ("On Freedom," 492–93). After all, a diminished understanding of the options brings with it an increased indifference toward those options.18 "If that is the freedom that we lack," she quips, "I do not think that we would have much to complain about" ("On Freedom," 493). In other words, she fully embraces the determination by perceived goodness as a perfection and as entirely compatible with freedom. In fact, it is more than just compatible with freedom: the most perfectly free actions are determined by what the agent perceives as good, as already seen. The lack of such determination is not something worth wanting.

2. suspending desires and mastering the passions

So far, we have seen strong evidence that Du Châtelet is a compatibilist: she claims explicitly that freedom is compatible with necessitation and that freedom is the capacity to do what one wills, rather than the capacity to will one thing or another. Yet, as already mentioned, she adds several layers of complexity to this picture that render her theory far more sophisticated than simple compatibilism. One layer of additional complexity is that she agrees with Locke and others about the importance of our ability to suspend our desires instead of acting on them immediately.

For Locke, the capacity for suspending desires is an extremely important aspect of human freedom and raises us above animals, who lack this capacity and are thus at the mercy of whatever desire happens to be strongest at the time.19 Note, however, that Locke is far from the only philosopher who discusses the importance of the ability to suspend desires, though he is perhaps most closely associated with it. Others include Leibniz and Descartes.20 Indeed, it makes good sense for [End Page 260] compatibilists to invoke the ability to suspend desires. After all, this doctrine is an appealing and straightforward way to explain how rational beings like us can sometimes refrain from acting on fairly strong passions or desires. More precisely, it is a plausible way of explaining how reason enables us to rise above our non-rational desires: instead of acting immediately and unreflectively on any whim or inclination that arises in us, we can take a step back from the situation and reflect more thoroughly before acting. Of course, we do not always reflect sufficiently before acting and, as a result, we often do things that we regret afterwards. Yet, the fact that we have the capacity to step back and reflect is clearly valuable and, arguably, central to our moral agency.

Du Châtelet gives the capacity to suspend our desires a prominent place in her theory of freedom:

We have the faculty of suspending our desires and of examining that which seems best to us, so as to be able to choose it: this is one aspect of our freedom. The power to then act in accordance with this choice makes this freedom full and whole; and when we make mistakes, we are using this power of suspending our desires badly and are determining ourselves too quickly.

According to this passage, freedom has two (and only two) aspects: the power of suspending desires while we examine the options further, and the power to act in accordance with the choice that results from that examination. This clearly goes beyond the simple compatibilism that we encountered earlier. It is important not just that we can do what we want, but also that we do not have to act immediately and unreflectively on any urge or desire. Yet, this additional element is a consistent extension of simple compatibilism because the suspension of desires need not be undetermined. Nothing in the view requires that we have the capacity to suspend desires indeterministically. The suspension might be determined psychologically.

Du Châtelet's insistence on the importance of rational reflection is indicative of a more general commitment to the priority of certain types of motives or desires over others. For Hobbes, there is no such priority: the will is whatever desire or aversion comes last in deliberation, and we are free whenever we act in accordance with our desires (e.g. Leviathan, 6.53, 33). Hobbes does not acknowledge a hierarchy of desires, or even a distinction between rational and non-rational desires (e.g. Questions, §28a, 83). For Du Châtelet, in contrast, it is clear that there is a hierarchy—and here she agrees with many other early modern philosophers.22 That is precisely why the power to suspend our desires is crucial: it is—at least sometimes—bad to act on certain types of desires. Hence, it is important that we can temporarily suspend such desires and, after more thorough reflection, adopt a better, more rational course of action. This suggests that freedom—at least in rational agents23—is first and foremost the power to act in accordance with rational judgments or rational choices.

That Du Châtelet endorses a hierarchical theory of desires is most explicit when she discusses the ways in which the passions can make us less free. In response to the [End Page 261] objection that we lack freedom because we are slaves to our passions, which make us perform actions of which reason disapproves, she admits that this is sometimes the case. Yet, she denies that we are hopelessly at the mercy of violent passions ("On Freedom," 486). She calls human freedom the "health of the soul" and says that while almost no person has a perfectly healthy soul, there are ways to improve its health ("On Freedom," 486–87). We can strengthen it through exercise, by "becoming accustomed to performing reflections and mastering our passions" ("On Freedom," 487).24 Even though we can never make reason the sovereign of all of our desires, we do possess a small degree of freedom ("On Freedom," 487). As this discussion makes clear, rational desires, or desires of which we reflectively approve, are privileged. Acting on some desire or other is not sufficient for freedom; we are only free to the extent that reason is master over the passions.25

I should note a small complication here. In one passage—the very last paragraph of "On Freedom"—Du Châtelet acknowledges that young children are free even though they lack reflection: "The freedom of children who never reflect consists only in willing and in performing certain motions" ("On Freedom," 502). This means that the ability to suspend desires in order to reflect on the options rationally, and more generally the ability to control one's passions through reflection, cannot strictly speaking be a necessary condition for freedom. Hence, it appears that, for Du Châtelet, freedom, broadly construed, does not require the capacity for suspending desires or mastering one's passions. Yet, this does not mean that Du Châtelet is contradicting herself with respect to the requirements for freedom. What she is saying in the passages about suspension and mastery, plausibly, is merely that it is important for our freedom—that is, the freedom of rational, adult human beings—that we can govern our actions rationally. We can view this as a more demanding type of freedom, which is more valuable than the simple freedom that is found in young children.26 In fact, in the passage under consideration, Du Châtelet explicitly notes that she is discussing the freedom of children, distinguishing it from the freedom of adults, which she defines one sentence earlier. It hence makes sense to read the majority of "On Freedom" as discussing the freedom of rational agents.

Before moving on, let us briefly examine how we might be able to reconcile what Du Châtelet says about the suspension of desires with her definition of freedom as the ability to act in accordance with one's choices. Are they entirely disparate elements of the theory? And, if so, why does she suggest that the latter is sufficient for freedom? One possibility, based on what I just said about the freedom of children, is, of course, to conclude that there are two different types of freedom: a broader type that does not require suspension or rationality, and a [End Page 262] narrower type that does. Another possibility, which I find even more promising, is that there is a deep connection between the ability of adult human beings to act in accordance with their choices—or more precisely, rational choices—and their ability to suspend desires. The two elements are not entirely disparate but rather two aspects of the capacity for acting rationally. After all, an agent cannot act rationally who is entirely at the mercy of her passions or non-rational desires. Such a passion-driven agent would never stop and deliberate about the best course of action, but would always act, unreflectively, on her instincts and passions. Hence, in the case of passionate creatures like us, the capacity for acting rationally requires both that the agent can control her passions to at least some extent, and that she can then act in accordance with her rational assessment of the options.

3. self-motion

A second—and more intriguing—layer of complexity that Du Châtelet adds to the simple compatibilist picture is the following: she places restrictions on the ultimate causes that a free action can have. For a simple compatibilist, it does not matter what ultimately causes a free action. Hobbes is again a helpful foil: what matters for him is simply that the action is caused proximately by the will. It does not matter whether something external was the ultimate cause of the volition and hence of the action. In fact, he holds that all actions are the products of causal chains going back to the beginning of the world (Leviathan, 21.4, 137). What makes an action free is merely that the last link in the chain before the action is a desire of the agent. Du Châtelet, in contrast, holds that such causal chains are incompatible with freedom. Instead, she insists that free actions must originate in a self-moving power of the agent.27 In other words, free agents must be agent causes of their free actions. Du Châtelet claims that this self-moving power is "the sole and true source of freedom" and that "insofar as man has this self-moving power, he is free" ("On Freedom," 493).

Du Châtelet clearly believes that causal chains would undermine freedom: during her discussion of divine foreknowledge, she notes that "it is not possible for us to conceive how God can foreknow future things, unless we suppose a chain of necessary causes" ("On Freedom," 498–99). As the context makes clear, she holds that such a chain would make human freedom impossible. After all, she goes on to admit that the best solution to the problem is that the apparent incompatibility between our freedom and God's foreknowledge stems only from our ignorance about God's attributes ("On Freedom," 499). In other words, she appears to be saying that there must be some way for God to foreknow our actions without a necessary chain of causes, even though we cannot conceive how precisely that works.

Before discussing Du Châtelet's account of self-motion more closely, it is helpful to note that references to a self-moving power also occur in Clarke's writings, in a very similar context. For instance, in his response to Collins's Inquiry, Clarke writes that [End Page 263]

Man either has within himself a Principle of Action, properly speaking; that is, a Self-moving Faculty, a Principle or Power of beginning Motion: Or he has not. If he has within himself such a Principle; then he is a Free, and not a Necessary Agent. For every Necessary Agent is moved necessarily by something else; and then that which moves it, not the thing itself which is moved, is the true and only Cause of the Action.

In other words, Clarke holds that, without a self-moving power, we would not be free because our actions would be the effects of something external to ourselves. They would be necessitated by causal chains. He makes a similar point earlier in the same text, adding that agency in general requires self-motion (Works, 4:729). In fact, as he explains in a response to John Bulkeley, even non-rational animals possess the power of self-motion, because self-motion is a prerequisite for any genuine activity: "the Spring of Action is The Self-Motive Power, which is (in All Animals) Spontaneity, and (in rational ones) what we call Liberty" (Works, 4:714).28 Clarke believes that the exercise of this self-moving power is not determined or necessitated by anything, not even the agent's perceptions or judgments. Hence, Clarke invokes the self-moving power to avoid determinism.29

Let us now examine Du Châtelet's claim that freedom requires a self-moving power in the agent more thoroughly and investigate whether it undermines my claim that she is a compatibilist. At first glance, it may appear to do so precisely because self-motion plays such a prominent role in Clarke's incompatibilist account of freedom. Yet, I will argue that Du Châtelet's self-moving power is best understood as compatible with determinism in much the same way in which Leibnizian spontaneity is compatible with determinism.

Du Châtelet does not say very much about the power of self-motion, and what she says is not easy to interpret. It first comes up during her discussion of liberty of indifference, in which she says that she is unsure whether the power to choose between two perfectly similar options "would be a perfection; but what is quite certain is that the self-moving power, the sole and true source of freedom, cannot be destroyed by the indiscernibility of two objects" ("On Freedom," 493). This passage may seem puzzling for multiple reasons. First of all, it appears that she is embracing something very similar to liberty of indifference, despite her extended criticism in the preceding paragraph: she appears to say that we have a power of moving ourselves, even with respect to two objects that are indiscernible to us.30 [End Page 264] Second, and relatedly, this passage appears to distinguish between the self-moving power and the power to choose. But why would she distinguish these two powers? Typically, philosophers who introduce a self-moving power identify it with the will, or with the power to choose.

I will return to the first puzzle later and start with the second puzzle. This puzzle is fairly easy to solve: the reason why Du Châtelet distinguishes between the self-moving power and the will is her rather unconventional theory of the will's nature. She holds that willing is simply a type of perception. This becomes clear just before her discussion of indifference: she says that "willing, judging etc. are nothing but different functions of our understanding" and that it is therefore a mistake to think of will and understanding as little beings that act on one another ("On Freedom," 492). She elaborates on this description of the will directly after she first introduces the self-moving power, defining the will as "the last perception or approval of the understanding" ("On Freedom," 493).31 Hence, Du Châtelet does not treat the will as a separate faculty; willing occurs in the understanding.

Moreover, and relatedly, she views the will as passive, like all functions of the understanding: "having perceptions and judging that a thing is true and reasonable … is not an action but a simple passion … and there is no connection between the approval and the action, between that which is passive and that which is active" ("On Freedom," 492). Because she calls the will an "approval" in the other passage, this means that the will is passive. In fact, it becomes clear elsewhere that the only active faculty for Du Châtelet is the self-moving power, or "the physical power of acting," as she calls it in that passage: "the privation of that power suffices by itself to turn man into a purely passive being, despite his intelligence" ("On Freedom," 494).32 Because of its passivity, the will can clearly not be identical to the self-moving power.

What, then, is the relationship between the will and the self-moving power? Does the will somehow prompt the self-moving power to act, and if so, how? Du Châtelet provides a surprising answer to that question: "the will, that is, the last perception or approval of the understanding, … cannot have any influence over the self-moving power, in which freedom consists" ("On Freedom," 493). At first blush, this can be taken to mean that there is no connection at all between the will and the self-moving power.33 Yet, for reasons that will become apparent later, [End Page 265] I think she merely means that the will does not efficiently cause the self-moving power's act. In other words, it does not efficiently cause the manifestation of the self-moving power.34 That makes sense, because the self-moving power would not be a self-moving power if it were moved by some efficient cause. In the continuation of the passage under discussion, we learn furthermore that "the will is never the cause of our actions" ("On Freedom," 493). This also makes sense, since the self-moving power is the power of acting, and its manifestations—that is, actions—are not efficiently caused by the will, as just seen.

Later in the same passage, Du Châtelet provides an additional reason why the will does not cause our actions: "an abstract notion cannot have any physical influence over the physical self-moving power that man possesses" ("On Freedom," 493). This is, again, reminiscent of Clarke, who asks rhetorically in his comments on Collins how "Reasons, Motives and Arguments, which are mere abstract Notions, can be the physical, necessary, and efficient Cause of Action" (Works, 4:723).35 Calling the will 'an abstract notion' may sound puzzling.36 Yet, recall that for Du Châtelet the will is simply a passive perception or approval occurring in the understanding. As such, it might amount merely to the perception that a particular option is the option one should pursue, or something along those lines. Hence, by 'abstract,' Du Châtelet might simply mean 'mental' or 'representational.' The will is a type of thought or perception. If that is correct, her point is that the mere thought that one should do something cannot efficiently cause the corresponding action.

It is clear, then, that on Du Châtelet's theory, the will does not efficiently cause actions. Yet, there must be some connection—and a rather tight one—between the will and the action. It would be strange indeed if what we do, even when acting with perfect freedom, had nothing to do with what we will and hence with what we judge to be best. Freedom is the ability to do what one wills, and this correspondence between will and action should presumably not be a mere lucky coincidence. Indeed, Du Châtelet says in the very same passage that there is a connection between the will and the action: "the will is never the cause of our actions, even though it is their occasion" ("On Freedom," 393). What might she mean by 'occasion'? She is clearly not an occasionalist; in other words, she cannot mean that on the occasion of an act of will, God causes the corresponding action or activates the self-moving power. She holds that the self-moving power is genuinely active and genuinely self-moving; it is not merely the locus of divine activity. So what else could she mean?

To answer this question, it is crucial to distinguish between 'occasional causation' and 'occasionalism.' The latter is the doctrine that God is the only efficient, productive, or active cause in the world; created things are merely occasions (or occasional causes) for God's activity. While this is the most famous usage of the notion of occasional causation, there are other usages. In fact, Clarke uses it in precisely the same context as Du Châtelet—that is, in order to describe [End Page 266] the relation between reasons and actions. As already seen, Clarke states that reasons and motives are abstract notions and hence cannot be efficient or physical causes of action. He then adds, "Occasions indeed they may be, and are, upon which That Substance in Man, wherein the Self-moving Principle resides, freely exerts its Active Power" (Works, 4:723).37 Hence, Clarke views motives or reasons as occasions not for divine activity, but for human activity. Yet, he does not explain what exactly he means by calling them occasions for the exercise of human self-motion; he merely says that it does not amount to physical or efficient causation. The same is true for some other early modern English authors who mention occasional causation.38 John Bramhall, for instance, states in his dispute with Hobbes that "outward objects … have no natural efficacy to determine the will. Well may they be occasions, but they cannot be causes of evil" (Defence, §14d, 52).39

Because the authors mentioned so far do not say what precisely occasional causation is, it is helpful briefly to examine a Cartesian usage of that notion. Steven Nadler describes this Cartesian understanding of occasional causation as follows. For a non-occasionalist substance dualist, there must be some sense in which what happens in the body can cause changes in the soul—for instance when damage in the body causes pain, or when the soul gains knowledge through its sense organs. Yet, on a Cartesian substance dualist picture, this causation cannot be efficient causation in the traditional sense. Such efficient causation would require a genuine or physical influence from cause to effect,40 which—for reasons that need not concern us here—is ruled out because of the radical dissimilarity between physical and mental states (Nadler, Occasionalism, 32).

To solve this problem, some Cartesians claim that the body can cause changes in the mind as an occasional cause, even though it cannot act as an efficient cause. Unlike efficient causation, occasional causation requires neither a substantial likeness nor a physical influence between cause and effect (Nadler, Occasionalism, 33). In what exactly does this kind of non-efficient causation consist? According to Nadler, occasional causation occurs "when one thing or state of affairs brings about an effect by inducing (but not through efficient causation …) another thing to exercise its own efficient causal power" (Nadler, Occasionalism, 33).41 On this view, [End Page 267] occasional causation is a genuine but sui generis and irreducible causal relation, which is governed by special causal laws (Nadler, Occasionalism, 37). That a thing is an occasional cause for a change in another thing is no mere coincidence; it is required by the relevant laws.

While the Cartesian notion is used to explain body-mind causation, Du Châtelet is concerned with the relation between an approval in the understanding and the corresponding action, which in many cases is a bodily motion.42 Hence, what Du Châtelet is worried about appears to be the converse of what Cartesians are typically worried about: mind-body causation, rather than body-mind causation. Nevertheless, the reasons why Du Châtelet invokes occasional causation may well be precisely the same as in the Cartesian case. Remember the problem that Du Châtelet faces: the correspondence between the will and the action cannot be purely coincidental. Yet, insofar as the action results from a self-moving power (and insofar as the will is passive), the will cannot be the efficient cause of the action. Moreover, she points to the radical dissimilarity between the will and the action: the will is an abstract notion and thus cannot have a physical influence over the self-moving power, or the power to cause physical motion ("On Freedom," 493).43

What Du Châtelet appears to be saying is this, then: because the will is "abstract" and the action is physical, there cannot be efficient causation between them. Hence, her reference to the will as an occasion might mean that the will prompts or induces the action of the self-moving power, but not as an efficient cause. It prompts in a non-productive way, without a physical influence. As already seen, this is also the Cartesian understanding of occasional causation. Maybe we cannot get any more specific than that—Du Châtelet does not spell out the precise nature of the causal relation in more detail. Yet, Du Châtelet is in good company here because that appears to be the case for Cartesian occasional causation as well. The causal relation is sui generis and hence cannot be reduced to other more familiar causal relations.

It also helps to note that something along these lines is central to many agent-causal theories: reasons, perceptions, judgments etc. plausibly have some connection to the action, even if the action is agent-caused and hence not the product of a chain of efficient causes. The agent causes the action without being caused to cause the action. Yet, the agent causes the action for a reason, that is, because of what the agent believes or desires. A complete disconnect between beliefs and action would be extremely implausible; to the best of my knowledge, no prominent proponent of agent causation endorses it.44 Hence, there is another respect in which Du Châtelet is in good company when insisting that prior mental states induce the agent to exercise her agent-causal powers, but do not efficiently cause the action.45 [End Page 268]

Of course, the fact that Du Châtelet puts forward an agent-causal theory of freedom may appear to undermine my claim that she is a compatibilist. After all, her description of the self-moving power sounds quite similar to agent-causal theories adopted by libertarians like Clarke and Thomas Reid. This brings us to the first puzzle that I mentioned earlier: it seems as if Du Châtelet ultimately accepts something very much like liberty of indifference. Yet, I do not think that her statements about the self-moving power force us to revise the claim that she is a compatibilist or that she rejects liberty of indifference. To see why, note first that a self-moving power is not the same as an undetermined power. The exercise of Du Châtelet's self-moving power is not efficiently caused by anything else—not even by beliefs, desires, or judgments of the agent. Yet, that does not mean that it is not determined by anything else. In fact, we saw earlier that Du Châtelet does appear to think that, at least in many cases,46 free actions are determined (or necessitated) by the agent's beliefs, desires, or judgments ("On Freedom," 496).

How can there be determination without efficient causation? In a way, we have already answered this: if Du Châtelet agrees with the Cartesian account of occasional causation, she holds that there is a non-efficient type of causation that can nevertheless be subject to deterministic laws. A short comparison with Leibniz will help us to understand this move, and its motivations, even better. After all, Leibniz also makes a certain type of self-motion or agent-causation central to his theory of freedom; he merely uses a different term: "spontaneity."47 The idea is very similar. A free action must originate in the agent; free actions cannot be products of causal chains. Motives or perceptions in the agent's mind influence the action, but they do not efficiently cause the action.48 Yet, Leibniz is definitely not a libertarian; he embraces determinism. And he can do so consistently because he holds that the nature of each substance—or its law of the series, as he sometimes calls it—determines all of the actions that the substance agent-causes.49

Moreover, it makes sense that agent causation is an attractive doctrine for compatibilists like Leibniz and Du Châtelet.50 After all, even a compatibilist may worry that, if our actions are products of efficient causal chains that originate outside of us, we are not genuinely free. According to this intuition, free actions must originate within us; we cannot merely be conduits for causal chains that happen to pass through us. That worry, however, is compatible with saying that given the agent's nature or character, or her beliefs and desires, those actions had to happen and are hence necessitated—though they are not efficiently caused [End Page 269] by anything but the agent. Hence, Du Châtelet's emphasis on self-motion is not convincing evidence for classifying her as a libertarian.

Another potential worry about Du Châtelet's claim that the self-moving power is "the sole and true source of freedom" ("On Freedom," 493) is that it is in tension with her definition of freedom as the freedom of action, or the power to do what one has chosen to do. How are we supposed to understand the relationship between those two definitions? What we have learned so far about self-motion suggests one plausible reason why Du Châtelet might think that the two definitions come down to the same thing: if it is metaphysically impossible for the will to cause the action because the will is an abstract notion, then perhaps the only way for an agent to act in accordance with her will—and thus the only way for the agent to possess freedom of action—is to exercise a self-moving power prompted by the volition. If my interpretation of self-motion is correct, Du Châtelet has excellent reasons for treating each of the two definitions as correct because they are necessarily co-extensional.

An additional potential worry about Du Châtelet's equation of freedom with self-motion concerns omissions. As we saw earlier, she says that "freedom consists in acting or not acting" and that freedom is "the power of thinking of one thing or of not thinking of it, of moving or not moving, in accordance with the choice of one's own mind." Presumably, this means that an omission can be free. Defining freedom as the ability to do what one has chosen can easily capture the sense in which omissions are free: an omission is free just in case it is in accordance with the agent's choice. After all, one can choose to refrain from doing something just as one can choose to do something. In contrast, it seems much more difficult to account for free omissions in terms of self-motion because omissions do not always appear to involve motion. That would be a problem insofar as Du Châtelet calls the power of self-motion "the sole and true source of freedom" and insists that "insofar as man has this self-moving power, he is free" ("On Freedom," 493). Admittedly, I am not sure how to solve this problem. It is possible that the account of freedom as self-motion is intended to work only for actions and not for omissions. In the philosophy of action, omissions are often special cases that require separate treatment. Hence, Du Châtelet may simply be bracketing them in her discussion of self-motion and focusing on what it means for agents to be free in their actions. She would hardly be the first or the last philosopher to do so.

Before moving on, one final question concerning the self-moving power is worth exploring: to what kind of motion is Du Châtelet referring when she talks about "self-motion"? There are two antecedently plausible options. First, it could be understood in the Aristotelian sense: the motion in question could be any type of change. Moving oneself in this sense merely means starting to act by oneself, without a prior efficient cause. On this first reading, Du Châtelet's claim that free agents possess a self-moving power simply means that they can move themselves to act or start new causal chains. For example, calling to mind a certain thought might be an exercise of this self-moving power even if it does not involve physical motion. Another possibility is that 'motion' is meant literally: it refers to genuine physical motion, that is, to motion in a body or bodies. On this second reading, attributing a self-moving power to free agents means that these agents have the capacity for causing physical motion without a prior efficient cause. [End Page 270]

There are some reasons to go with the first reading, according to which self-motion does not need to involve literal physical motion. After all, the very first definition of freedom that Du Châtelet provides in "On Freedom" is this: "I call freedom the power of thinking of one thing or of not thinking of it, of moving or not moving, in accordance with the choice of one's own mind" ("On Freedom," 485). Similarly, a few pages later, she asserts that "we have the power of acting, of moving our body, of applying our mind to certain thoughts, of suspending our desires etc." ("On Freedom," 487). Thus, Du Châtelet seems to hold that both the power to effect changes in one's thoughts and the power to move one's body are important for freedom. This might suggest that when she later discusses the power of self-motion as the "sole and true cause of freedom" ("On Freedom," 493), she is using 'motion' to cover both changes in thought and changes in physical location.

Yet, there are also indications that the self-moving power is meant to refer specifically to the power to effect physical motion. First, as already seen, she sometimes appears to refer to the self-moving power as the "physical power of acting" ("On Freedom," 494) and the "physical self-moving power" ("On Freedom," 493). More intriguingly, she says the following in a letter to Pierre Maupertuis dated April 30, 1738:

the only thing that puzzles me at present is freedom, because I believe that I am free and I do not know if this quantity of forces, which is always the same in the universe, does not destroy freedom. Does initiating motion [commencer le mouvement] not mean producing in nature a force that did not exist? Yet, if we do not have the power to initiate motion, we are not free. I beg you to enlighten me on this point.

In this passage, Du Châtelet claims that the power to begin motion is a necessary condition for freedom and she explicitly equates that power with the production of a new force in the physical world. That is precisely what she says puzzles her so much: how is freedom compatible with the physical law of the conservation of force? If we are free, she is suggesting, then the overall amount of force in nature cannot remain the same because free actions introduce new forces.

Understanding the self-moving power as the power to cause physical motion would also help explain why Du Châtelet says that the will is not the cause but only an occasion of our actions since "an abstract notion cannot have any physical influence over the physical self-moving power that man possesses" ("On Freedom," 493). The reason why the will cannot influence the act of the self-moving power physically might be that the will is a mental state while the action is a physical event. In fact, that fits extremely well with my explanation for why she invokes occasional causation: like the Cartesians, she plausibly invokes occasional causation to bridge the mind-body divide. For these reasons, it seems most plausible to me that Du Châtelet thinks of the self-moving power (at least primarily) as the power to cause physical changes.

4. moral necessity

A final layer of complexity is Du Châtelet's claim that while free actions cannot be physically or absolutely necessitated, they can be morally necessitated. This may [End Page 271] initially sound like an attempt to soften or even repudiate compatibilism, but I will argue that, on reflection, it is not. The most central passage in which Du Châtelet discusses moral necessity deserves to be quoted in full:

It is true, it would be a verbal contradiction, morally speaking, [to say] that a being that we suppose to be wise does something ridiculous; as a result, such a being certainly prefers that which its understanding judges to be the best. Yet, there would not be any physical contradiction in this, because one must carefully distinguish between physical necessity and moral necessity. The former is always absolute, but the latter is always contingent. And this moral necessity is entirely compatible with the most perfect natural and physical freedom.

Her point here appears to be that it is morally impossible, but physically possible, for a wise being to do something unwise. Or, in other words, it would be a moral contradiction but not a physical contradiction.51 Moreover, she stresses that moral necessity is compatible with freedom—more specifically, with what she here calls "physical freedom," presumably because it involves a physical contingency.52 She mentions moral necessity in a few other places as well: she says, "The moral necessity of always doing the best is even all the greater in God" ("On Freedom," 495) and that "This necessity of always doing the best can only ever be a moral necessity, but a moral necessity is not an absolute necessity" ("On Freedom," 496).

Du Châtelet does not elaborate on the distinction between moral and physical necessity, presumably because the distinction was already well established. The term has a long and complex history,53 but Clarke and Leibniz are likely sources of influence on Du Châtelet here. Let us first take a look at Clarke,54 who uses this notion in several texts. In his second response to Bulkeley, Clarke distinguishes between "Moral Contradiction and Moral Necessity" on the one hand, and "Natural Contradiction and Natural Necessity" on the other (Works, 4:716). To illustrate this distinction, he grants—using the same example as Du Châtelet—that it is "a Contradiction in Terms, Morally speaking, that a Wise Man should do a Foolish Thing, or an honest Man a dishonest Thing: But it is no Contradiction in Physics" (Works, 4:716). As Clarke stresses in his response to Collins's Inquiry, moral necessity is not strictly speaking a type of necessity at all; it is merely a figurative way of speaking, which "has nothing at all of Physical Reality in it" (Works, 4:725). He makes the same point in his "Fifth Letter to Leibniz" (Works, 4:673). According to these passages, something is morally necessary for an agent when that agent's character traits—her wisdom, goodness, veracity etc.—prevent her from acting differently, but nothing physical prevents her from acting differently. And unlike physical necessity, moral necessity is perfectly compatible with freedom.

In his Boyle lectures, Clarke employs the notion of moral necessity slightly differently, namely, to describe the connection between the judgment that there are strong reasons to do something and the corresponding action. His [End Page 272] example is a mentally healthy man who "judges it unreasonable for him to Hurt or Destroy himself," and who consequently—being neither compelled nor tempted externally—"cannot possibly act contrary to this Judgment; not because he wants [i.e. lacks] a Natural or Physical Power so to do, but because 'tis absurd and mischievous, and morally impossible, for him to Choose to do it" (Works, 2:565). Clarke adds that for the same reason, perfectly rational agents cannot act against their knowledge of what is best. Yet, he insists, this kind of necessitation—which is not strictly speaking necessitation at all—does not undermine freedom. Here, 'moral necessity' describes the influence of strong reasons on a rational mind.55

Leibniz also discusses moral necessity at length in several of his later writings, including the Theodicy and his correspondence with Clarke, both of which would have been easily available in 1730s France.56 Like Clarke, Leibniz often describes moral necessity as the determination of a wise or rational mind by persuasive reasons. Or, to put it slightly differently, he defines it as the determination of a mind by its judgments about the good. For instance, he writes to Clarke that moral necessity is that "by which a wise being chooses the best and every mind follows the strongest inclination" (Correspondence, 5.4, 36). Like Du Châtelet, Leibniz insists that God is morally necessitated to do what is best, but that he is not absolutely necessitated; absolute necessity would undermine freedom, but moral necessity does not.57

While it is controversial what precisely Leibnizian moral necessity amounts to, I have argued elsewhere58 that it is not supposed to be a weaker kind of determination than absolute, physical, or metaphysical necessity. Rather, it is merely a determination or necessitation with a different source. Unlike Clarke, Leibniz is often quite content to say that moral necessity is a genuine type of necessity or determination; he sometimes calls it a "happy necessity" (e.g. Theodicy, §175; §191; §344). Admittedly, he does sometimes stress that free agents are not necessitated by their judgments or motives, but as he makes clear in some places, he means merely that they are not necessitated metaphysically.59 Moral necessitation is simply a determination by what the agent takes to be good, rather than by something value-neutral or independent of perceived goodness.60 If this interpretation is correct, Leibnizian moral necessitation is compatible with determinism whereas Clarkean moral necessitation is not.61 [End Page 273]

Interestingly, Leibniz is not the only philosopher in this milieu who understood moral necessity in a determinism-friendly way. Collins also does this; he says in the preface to his Inquiry,

when I affirm necessity; I contend only for what is call'd moral necessity, meaning thereby, that man, who is an intelligent and sensible being, is determin'd by his reason and his senses; and I deny man to be subject to such necessity, as is in clocks, watches, and such other beings, which for want of sensation and intelligence are subject to an absolute, physical, or mechanical necessity.

In other words, Collins's moral necessity is simply the determination of agents by motives; it is distinguished from other types of necessitation merely with respect to the source of the determination.62

If Du Châtelet shares the view that I am attributing to Leibniz, her claim that free actions are only morally necessary does not give us reason to doubt that she is a compatibilist.63 After all, the distinction between moral and absolute necessity, understood in this way, is a thoroughly compatibilist distinction: it is merely the distinction between sources of necessitation that are compatible with freedom and sources that are not. Freedom, on this view, is compatible with determinism because free agents can be necessitated by their judgments about the good. In fact, there is evidence that this is how Du Châtelet understands moral necessity: in response to the objection that God is not free because he is necessitated by his nature to do the best, she simply asks, "is there another type of freedom [than to be necessitated to do what one wills to do]?" ("On Freedom," 495). More generally, she embraces the necessitation by the good as a perfection, as seen earlier. This way of understanding moral necessity fits extremely well with the previously discussed elements of her theory freedom: the claim that free actions can only be necessitated morally is merely a restatement of the claim that free actions must be prompted by the agent's judgments about the best course of action.

5. some potential objections to a compatibilist reading

So far, we have seen strong evidence that Du Châtelet is an agent-causal compatibilist: freedom requires self-motion but is nevertheless compatible with necessitation. Before closing, I will briefly respond to two potential problems for this reading. One potential problem is that Du Châtelet seems quite uncertain how best to reconcile human freedom with divine foreknowledge in "On Freedom" and eventually concludes that we simply cannot understand how God can foreknow our free actions. One might think that it should be relatively easy for a compatibilist to explain divine foreknowledge and that this uncertainty is therefore evidence against a compatibilist reading. Another potential problem stems from Du Châtelet's letters to Maupertuis, in which she repeatedly raises the worry that human freedom would involve the violation of physical laws. That, too, may look like evidence against a compatibilist reading. [End Page 274]

With respect to divine foreknowledge, a close look at the relevant passages reveals that the worry Du Châtelet is addressing is a worry that makes sense for an agent-causal compatibilist: she worries that God somehow influences or causes our actions. This becomes clear in a passage already quoted earlier: "it is not possible for us to conceive how God can foreknow future things, unless we suppose a chain of necessary causes" ("On Freedom," 498–99). Apparently, what she is concerned about is that God's foreknowledge would undermine the self-motion of human agents by efficiently causing or absolutely necessitating their actions. But why? One might think that God should be able to foresee what his creatures will freely agent-cause, based simply on his knowledge of their natures and the relevant laws.64

My suggestion is that Du Châtelet's worry is the following: God's creating and providentially ordering the world is the ultimate cause of everything else; it is through his own planning and acting that God foreknows what his creatures will do. While there is strictly speaking no continuous chain of efficient causes, there is a chain of sorts: God efficiently causes finite agents to exist, and they in turn cause their actions in a way that is determined (at least in many cases) by their natures and circumstances. Moreover, there may be a chain of determination: the way God creates us determines how we (often) act. Hence, it may seem that God is the ultimate cause and determiner of human actions and that human beings are elaborate divine puppets. It makes perfect sense for Du Châtelet to worry about this kind of chain, even though she is a compatibilist. In fact, Leibniz also worries that divine providence might make God the ultimate author of all creaturely actions (see, e.g. Theodicy, §3).

Let us now turn to Du Châtelet's letters to Maupertuis. In the context of discussing the Leibnizian doctrine of living forces (forces vives) and the related doctrine that the universe always contains the same quantity of force, she expresses the worry that freedom requires the violation of the laws of nature. In the letter of April 30, 1738 that I quoted earlier, she asks Maupertuis to explain how we can possibly be free if the quantity of force in the universe is conserved.65 After all, she says, freedom requires the ability to begin a new motion, which in turn consists in "producing in nature a force that did not exist" (Les lettres, 1:220–21/Selected Writings, 109, my translation). Hence, she says, freedom seems incompatible with the law of the conservation of force.

Just nine days later, she sends another letter to Maupertuis (dated May 9, 1738), tentatively suggesting a solution to the worry:

If you do not believe that I am free, I would be quite distressed. … I would like to act as conciliator for a moment … and say that God could have established laws of motion for the impact of inanimate bodies through which they conserve or transfer or use in their effect the force imprinted on them, but that this does not rule out [End Page 275] the existence of a self-moving power in animate things,66 which like intelligence, life etc. is a gift from the creator. For if I am free, it must absolutely be the case that I can initiate motion, and if my freedom were demonstrated it would be quite fitting [convenir] that my will produces some force whose 'how' is hidden from me.67

Like in the first letter, Du Châtelet claims here that the law of the conservation of force seems incompatible with freedom because freedom requires the ability to initiate a new motion. It is interesting that the conciliatory suggestion that Du Châtelet appears to be making is very similar to her preferred solution to the foreknowledge problem: we cannot ultimately understand how freedom is compatible with the laws of motion, but perhaps that is simply due to our limitations. God could have given us a power whose operations we cannot fully understand.

But why would Du Châtelet worry that the laws of motion undermine freedom if, as I have argued, she is a compatibilist? The entire point of compatibilism, one might think, is that freedom does not require the violation of natural laws. One possibility is that Du Châtelet changed her mind about freedom between "On Freedom" and the letters to Maupertuis. Perhaps she came to think of the self-moving power as an indeterministic power. There was not a huge amount of time between her composition of "On Freedom" and the letters to Maupertuis, but that is not a strong reason to rule out a change of mind. Du Châtelet was only starting to develop her views on physics and metaphysics during that period. Yet, there is reason to doubt that a change of mind is the best explanation for the worry expressed in the letters to Maupertuis. In her Foundations of Physics, first published in 1740, she says something about freedom that suggests she is still a compatibilist: God freely chose to create the world that pleased him the most because "to act following the choice of one's own will is to be free" (IP §25/Selected Writings, 143). This definition of freedom sounds very much like the compatibilist definitions that I discussed earlier.

Indeed, when we pay closer attention to Du Châtelet's theory of action, it becomes clear that there is no need to assume a change of mind. The two texts are entirely consistent; it makes sense for someone endorsing the views of "On Freedom" to worry that the laws of motion undermine freedom. To see why, recall the way in which Du Châtelet describes the self-moving power and the relation between the agent's will and the action in "On Freedom." She stresses that the will cannot cause our actions because "an abstract notion cannot have any physical influence over the physical self-moving power that man possesses"; instead, the will [End Page 276] merely occasions the action ("On Freedom," 493). Hence, the will's influence on the action is not a physical influence. A physical entity—namely, a bodily motion or force—has as part of its explanation something non-physical and not subject to the laws of physics, namely, a mind or a mental state. There is no purely physical explanation for the new physical force that comes into existence.68 This does not mean, however, that this physical event is undetermined; it merely means that it is not determined physically—it may well be determined psychologically. In fact, that is arguably what Du Châtelet means by saying that free actions can be necessitated morally but not physically.

On reflection, it is not surprising that, for Du Châtelet, an action cannot be free if it is determined by events in the physical world. Since freedom requires self-motion, free actions cannot be the products of causal chains like the chains of physical causes that are covered by the laws of motion. Thus, the letters to Maupertuis simply point to a tension between the claims about self-motion in "On Freedom," on the one hand, and a commitment to an exceptionless law of the conservation of force, on the other hand.69 There is no good reason to doubt that Du Châtelet still subscribes to the compatibilist views expressed in "On Freedom" when writing to Maupertuis.

One worry about this interpretation might be that it seems incompatible with Du Châtelet's broadly Leibnizian metaphysics according to which all reality ultimately consists of monads.70 On that picture, the laws of physics must ultimately be grounded in the laws that govern monads, and hence, it may appear that the two cannot come into conflict. I am not entirely sure that a monadological metaphysics does in fact rule out the type of conflict described in the Maupertuis letters; for Du Châtelet, as for Leibniz, the relationship between the laws of physics and the laws that govern the fundamental monadic level is far from straightforward. Yet, even if such conflict is ruled out, it does not matter for present purposes because there are good reasons to think that Du Châtelet's monadological metaphysics was not yet in place when she wrote the letters to Maupertuis in April and May 1738. It appears that when she started working on the Foundations of Physics in 1737, she had not yet adopted a fully monadological metaphysics; that seems to have happened only in late 1738 or early 1739, when she started a radical revision of the Foundations, adding more detailed discussions of Leibnizian metaphysics.71 Indeed, she writes to Maupertuis on February 10, 1738 that "Mr. Leibniz was only right about living forces," not about his other doctrines (Les lettres, 1:217). Hence, it seems that we do not need to reconcile the Maupertuis letters with the monadological picture that we find in the 1740 Foundations. One can even speculate that the reason why [End Page 277] Du Châtelet chose not to include "On Freedom" in the published version of the Foundations is that she had come to adopt a metaphysics that does not fit entirely with the views defended in "On Freedom."72

6. conclusion

I have argued that Du Châtelet's theory of freedom is best interpreted as a form of agent-causal compatibilism. She holds that freedom requires self-motion but that this self-motion can be necessitated by the agent's judgment. More specifically, Du Châtelet puts forward a theory of freedom with the following elements: (a) freedom consists in the power to act in accordance with one's choices, (b) freedom requires the ability to suspend desires and master passions, (c) freedom requires self-motion, and (d) freedom is compatible with moral necessity but not with physical necessity.

Even though these different elements may seem disparate, we saw that they fit together quite nicely. Freedom is the ability to act in accordance with one's choices. Since these choices must be based on a rational assessment of the options, freedom also requires the ability to suspend desires and master the passions. If an agent always acts on her strongest passion and is unable to assess the options rationally before acting, she is not free. Moreover, since the will cannot exert an efficient-causal influence on the action, acting in accordance with one's choices—and hence freedom—requires self-motion. Finally, since the will is the understanding's approval of a course of action, free actions can only be morally necessary, that is, they can only be necessitated by the (apparent) goodness of the object of choice. If an action is necessitated in a way that does not depend on perceived goodness, the action is not free.73

Julia Jorati

Julia Jorati is Associate Professor of Philosophy at The Ohio State University.

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Stan, Marius. "Emilie du Châtelet's Metaphysics of Substance." Journal of the History of Philosophy 56 (2018): 477–96.
Wade, Ira O. Studies on Voltaire: With Some Unpublished Papers of Mme du Châtelet. Princeton: Princeton University Press, 1947. [Studies on Voltaire]
Yenter, Timothy, and Ezio Vailati. "Samuel Clarke." In The Stanford Encyclopedia of Philosophy, edited by Edward N. Zalta, URL =, 2017.
Zinsser, Judith P. La dame d'esprit: A Biography of the Marquise Du Châtelet. New York: Viking, 2006. [Biography]


1. See, e.g. Ira Wade, Studies on Voltaire, 88–90. "On Freedom" is included in the Oeuvres complètes de Voltaire, as an appendix to the Treatise of Metaphysics.

5. To name just a few examples of major differences, Voltaire's Treatise does not mention moral necessity and insists that a necessary determination of the will would undermine freedom. As we will see below, Du Châtelet claims the opposite and stresses moral necessity several times. Moreover, as we will see in sect. 3, Du Châtelet views the will as a function of the understanding—a doctrine that we do not find in Voltaire's Treatise. Finally, Voltaire's discussion of the power of agents to move is quite different from Du Châtelet's theory of self-motion. While Voltaire merely mentions that free agents can determine themselves or move in accordance with their wills, Du Châtelet invokes a physical self-moving power and describes in quite some detail how that power relates to the will and to the action.

6. One exception is Marcy Lascano, who devotes a section in a longer unpublished chapter to Du Châtelet's theory of freedom ("Émilie Du Châtelet"). There is also some cursory discussion of "On Freedom" in the Voltaire literature, by scholars who believe it to be written by Voltaire. See, e.g. Wade, Studies on Voltaire, 92–94.

7. These Clarkean elements are among the main differences between the theory of freedom put forward in "On Freedom" and Voltaire's account in his Treatise of Metaphysics.

8. For a helpful general discussion of Clarke's influence on Du Châtelet (though without mentioning his influence on her theory of freedom), see Sarah Hutton, "Du Châtelet and Clarke."

9. One good example is the dispute between Clarke and Anthony Collins (see, e.g. Collins, Inquiry, and Clarke's response in Works, 4:721–40). The question of whether free actions are necessitated is front and center in their dispute.

10. There is no published English translation of "On Freedom," so all translations from that text are mine. In general, I will cite English editions when available. If an English edition is explicitly cited, translations are taken from that edition, unless otherwise specified. If no English edition is cited, translations are mine.

11. I do not think that this definition is best read as invoking a two-way power, that is, as claiming that in order to be free in a particular situation, an agent must possess both the power to φ and the power not to φ. Rather, I understand this passage as claiming merely that a free agent can act in accordance with their choice. If the agent has chosen to φ, then freedom requires that the agent is able to φ; if the agent has chosen not to φ, then freedom requires that the agent is able to refrain from φ-ing. If Du Châtelet thought that freedom requires a two-way power, or the ability to do otherwise, it would be extremely strange that she does not say that more explicitly in "On Freedom." Most of her definitions and discussions focus on the agent's ability to do what he has chosen or what appears best to him. Moreover, as we will see soon, she holds that freedom is compatible with necessitation.

12. This fits with what she says in her Foundations of Physics: "to act following the choice of one's own will is to be free" (IP §25/Selected Writings, 143).

13. For Hobbes's definition, see, e.g. Leviathan, Chapter 14, Paragraph 2, 79 and 21.1–2, 136. Citations from Leviathan are according to chapter, paragraph, and page number in Edwin Curley's edition. See also Collins, Inquiry, ii and 116–17; and Locke, Essay, Book II, Chapter xxi, Sections 8 and 10. Citations from the Essay are according to book, chapter, and section number in Peter Nidditch's edition.

14. See, e.g. Hobbes, Leviathan, 21.2, 136; Questions, Section 1c, 72 and §38, 88–89; and Locke, Essay, II.xxi.10. Citations from Questions are according to section and page number in Vere Chappell's edition.

15. It is true that, in the passages just quoted, Du Châtelet ascribes to God a necessity with respect to acting and to human beings with respect to willing. Yet, it will become clear later that this does not ultimately point to a difference between divine and human freedom. Du Châtelet appears to hold that the necessitation of both the will and the action is compatible with freedom, both for human beings and for God. One difference is, of course, that human beings are frequently unable to do what they have chosen to do; they are not omnipotent. That might be the reason why Du Châtelet does not ascribe a necessity of doing what they judge to be best to humans. Another reason might be the influence of passions on human actions.

16. Here Du Châtelet is siding with Collins and not with Clarke; see Collins, Inquiry, 67–68; and Clarke, Works, 4:731.

17. The question of whether agents can choose among indiscernible options is very central to the correspondence between Leibniz and Clarke. Leibniz answers that question negatively while Clarke answers it affirmatively. See Leibniz, Correspondence, Letter 4, Section 1, 22; Clarke, Works, 4:672. Citations from Leibniz's Correspondence are according to letter, section, and page number in Roger Ariew's edition.

18. This objection does not seem to work against sophisticated proponents of liberty of indifference. E.g. on Francisco Suárez's theory, indifference is not increased by a lack of knowledge (see, e.g. Disputations, Disputation 19, Section 5, Paragraphs 15–16 and 19.4.4). Citations from the Disputations are according to disputation, section, and paragraph number in Alfred Freddoso's edition.

20. See, e.g. Leibniz, New Essays, Book II, Chapter xxi, Section 47, 195–96; Theodicy, §327; and Correspondence, 5.11, 37–38. Citations from the New Essays are according to book, chapter, section, and page number in Peter Remnant and Jonathan Bennett's edition. See also Descartes, "Fourth Meditation" (AT VII.61–62/CSM II.43); and Principles, I.6 (AT VIIIA.6/CSM I.194). Note that, in these texts, Descartes talks of suspending or withholding judgment, not desire. Yet, that terminological difference is not ultimately significant because, for Descartes, the will is involved in judgment; when we withhold judgment, we withhold the will's act of assent. In his late work Passions of the Soul, Descartes does discuss the importance of ridding oneself of "less useful desires" in order to reflect more thoroughly on what is genuinely good; see Passions, §144 (AT XI.437/CSM I.379). Yet, he also notes there that we often cannot suspend passions directly but must instead conquer them indirectly; see Passions, §§45–48 (AT XI.362–67/CSM I.345–47).

21. She also mentions the power to suspend a few pages earlier. See "On Freedom," 487.

23. As we will see soon, Du Châtelet appears to hold that young children who are not yet rational can be free in a different sense.

24. It is interesting that this rather negative assessment of the passions appears to contrast with Du Châtelet's discussion of the passions in her much later essay "Discourse on Happiness" (Selected Writings, 345–65). There, she argues that satisfying one's passions is crucial for happiness and the good life.

25. This talk of mastering the passions is found in other early modern authors as well, e.g. in Leibniz (New Essays, II.xxi.35, 188 and II.xxi.47, 196) and Descartes (Passions, §50 [AT XI.370/CSM I.348]). It is of course even more prominent in ancient—particularly Stoic—philosophy.

26. Clarke also claims that children are free even though in them, freedom is not joined with an understanding of "moral Good and Evil." While the freedom of adult humans is "eminently called Liberty," children possess "the same physical Liberty" that adults possess (Works, 4:729).

27. Du Châtelet uses the terms pouvoir soi-mouvant or pouvoir physique soi-mouvant for this power ("On Freedom," 493); these terms are seemingly synonymous with pouvoir physique d'agir ("On Freedom," 494).

28. Clarke says something very similar in his fifth letter to Leibniz (Works, 4:671). In his response to Collins's Inquiry, Clarke even says that self-motion in non-rational animals is a type of freedom (Works, 4:729).

29. For textual evidence, see, e.g. Works, 4:723; 4:725; and 4:673. I should note that, while Clarke is typically interpreted as a libertarian (see, e.g. James Harris, Of Liberty and Necessity, 13 and 46–53), it is not entirely clear to me that this is correct. Timothy Yenter and Ezio Vailati, "Samuel Clarke," also note that there are compatibilist elements in Clarke's theory though they portray him as a libertarian. Even though Clarke denies that free actions are determined or necessitated by perceptions or reasons, it sometimes sounds as if he merely means to rule out efficient causation. He sometimes acknowledges that there is a clear sense in which the agent cannot do otherwise. Hence, it is worth asking whether the difference between him and Du Châtelet (as well as Leibniz) is ultimately merely verbal. Yet, I will ignore this complication for the rest of this paper because it would take us too far afield. Going forward, I will assume that the standard interpretation of Clarke as a libertarian is correct.

30. Here, Du Châtelet agrees with Clarke, who, in the "Fifth letter to Leibniz," also states that "a Free Agent, when there appear two, or more, perfectly alike reasonable Ways of acting; has still within itself, by virtue of its self-motive Principle, a Power of acting" (Works, 4:672). Leibniz disagrees vehemently (see, e.g. Theodicy, §8; §196; and Correspondence, 5.16–19, 39). Incidentally, Du Châtelet's claim about our ability to act even when we cannot discern differences among the options suggests that, when writing "On Freedom," she is not a global determinist and does not embrace a strong version of the Principle of Sufficient Reason. Since Du Châtelet appears to embrace a strong version of the Principle of Sufficient Reason in her Foundations of Physics (IP §8/Selected Writings, 128–31), she must have changed her mind about this after writing "On Freedom." Note, however, that being a global determinist is not a requirement for compatibilism.

31. This definition of the will is very similar to the one that Bulkeley puts forward in his correspondence with Clarke. Bulkeley there defines the will as "the last Judgment of the Understanding" (Clarke, Works, 4:713). Clarke disagrees with this definition, stressing that while the last judgment of the understanding is passive, the volition must be active (Works, 4:717; but cf. Works, 2:565).

32. Incidentally, this quotation is similar to a passage from Clarke (Works, 4:729). The passivity of the will provides us with another reason why freedom cannot be in the will: as becomes clear elsewhere, Du Châtelet opposes freedom to passivity ("On Freedom," 489).

33. This is even confirmed by a passage already quoted in the previous paragraph, in which Du Châtelet claims that "there is no connection [liaison] between the approval and the action" ("On Freedom," 492).

34. For more on the term 'influence' and its association with efficient causation, see below.

35. Clarke says something along similar lines a few pages later (Works, 4:734; see also 4:728).

36. Harris, in his discussion of Clarke's claim that motives are abstract notions, also admits that this is unclear (Of Liberty and Necessity, 59). Yenter and Vailati interpret Clarke's abstract notions as propositions ("Samuel Clarke").

37. It is interesting that in his Boyle Lectures, Clarke uses slightly different terminology to make what appears to be the same point: "the Beginning of Action, consequent upon the last Judgment of the Understanding, is not determined or caused by that last Judgment, as by the physical Efficient, but only as the Moral Motive. For the true, proper, immediate, physical Efficient Cause of Action, is the Power of Self-motion in Men" (Works, 2:565). He then stresses that the connection between the last judgment of the understanding and the action is merely morally necessary (Works, 2:565). This is very helpful because it points to a connection between occasional causation and the notion of moral necessity, which I will discuss in sect. 4.

38. In the introduction to his book on free will in eighteenth-century British philosophy, Harris notes that invoking occasional causation was a common strategy for avoiding necessitarianism (Of Liberty and Necessity, 7).

39. Similarly to Clarke (see n. 37), Bramhall goes on to say that the connection between appetite and action is at most morally necessary.

40. Suárez, whose treatment of efficient causation was extremely influential in the early modern period, helpfully explains that a physical influence is "that which is effected through true, real, proper, and per se causality" (Disputations, 17.2.6).

41. Descartes invokes occasional causation, e.g. in Comments on a Certain Broadsheet (AT VIIIB.359/CSM I.304) and in the authorized French translation of the Principles (AT IXB.64).

42. As Nadler points out, the causal relata of occasional causation are the occasion and the entity that results from the substance's exercise of its causal powers (Occasionalism, 33).

43. As we already saw, the term 'physical influence' is a traditional term for the real influence of an efficient cause; see n. 40.

44. In a way, Du Châtelet's theory faces a challenge similar to the challenge that incompatibilists face: to show how something can explain an action without being a deterministic efficient cause of the action. For more on reasons explanations in agent-causal theories of freedom, see Meghan Griffith, "Agent Causation," 75–76.

45. William Rowe discusses Clarke's response to this problem ("Causality and Free Will," 60).

46. An exception are cases in which the agent cannot perceive any differences between the options she is facing; in such cases, Du Châtelet seems willing to say that the agent can choose without being determined by her perceptions ("On Freedom," 493). That does not undermine her compatibilism, however, because compatibilism is merely the view that freedom is compatible with determinism; compatibilists do not have to hold that determinism is true or that all free actions are determined.

47. See, e.g. Theodicy, §288.

48. This is somewhat controversial, but I argue for it elsewhere (e.g. Jorati, Leibniz on Causation and Agency, 30–32).

50. I discuss the reasons why it may be attractive to compatibilists in Jorati, Leibniz on Causation and Agency, 117–19. See also Ned Markosian, "Agent Causation," who argues that compatibilists should embrace agent-causation because it solves the main problems that traditional compatibilism faces.

51. Like Leibniz, Du Châtelet understands possibility as non-contradictoriness and necessity as that whose opposite implies a contradiction; see IP §5/Selected Writings, 127.

52. Clarke also uses the term 'physical liberty' in several texts, apparently viewing it as the absence of physical necessity; see, e.g. his response to Collins's Inquiry (Works, 4:425 and 429).

54. Harris provides a helpful discussion of Clarke's treatment of moral necessity (Of Liberty and Necessity, 46–53).

55. This usage is compatible with Clarke's other usages of the term, since we can simply view rationality as one of the character traits that can morally necessitate the corresponding actions.

56. Du Châtelet asked her bookseller to send her a copy of the Leibniz-Clarke correspondence in February 1739 (Les lettres, 1:329). Yet, that does not necessarily mean that she did not read it before then; Voltaire may have brought his copy to Cirey, e.g. For more details on Du Châtelet's acquaintance with Clarke's writings, see Hutton, "Du Châtelet and Clarke."

59. See, e.g. Theodicy, §230; §132. Arguably, we can read this into other passages in which he claims that free actions are determined but not necessitated (e.g. Theodicy, §367; §310; New Essays, II.xxi.13, 178 and II.xxi.49, 199). In any case, Leibniz seems perfectly happy to acknowledge that free actions are determined by motives. In contrast, Clarke stresses that motives do not determine or necessitate; when we say that they do, we are speaking improperly or figuratively (see, e.g. Works, 4:723; 4:725; and 4:673).

60. Importantly, it is not a determination by efficient causes but by final causes. Hence, moral necessity is a type of necessitation that is compatible with agent causation, and with the claim that free actions are not products of efficient-causal chains.

61. For some textual evidence, see n. 59.

62. See Harris, Of Liberty and Necessity, 55, for a more detailed discussion of Collins's usage of moral necessity.

63. By 'physical necessity,' Du Châtelet presumably means a necessitation through efficient-causal chains or through the laws of physics.

64. Of course, this would not work in cases where human beings use self-motion to take one of multiple indiscernible options. Yet, those are not paradigmatic—or particularly valuable—exercises of free agency. It is hence unlikely that they are at the center of Du Châtelet's worries about foreknowledge.

65. She already hints at this problem in an earlier letter to Maupertuis, written on February 10, 1738. There, she raises a number of concerns about the claim that the total quantity of force in the universe never changes; one of these concerns is that free creatures would then not be able to initiate motion (Les lettres, 1:217).

66. It is not clear that this means that all animate things have a self-moving power. It might merely mean that exceptionless laws of motion leave open the possibility of a self-moving power in animate things. Yet, holding that all animate things possess the power of self-motion would be in line with Clarke's view; see n. 28.

67. Ruth Hagengruber appears to interpret this passage as ironic: she writes that "With astounding wit, [Du Châtelet] points out just how improbable [positing two separate laws of motion, one for animate and one for inanimate things] would be" (Hagengruber, "Transformation," 41). Yet, I do not think the suggestion is meant ironically; Du Châtelet seems willing here, as she is in "On Freedom," to take refuge in divine mystery to some extent and to acknowledge the possibility that we cannot fully understand everything. I take her effort at conciliation to be entirely serious.

68. It is worth noting that, in his "Fifth Letter to Leibniz," Clarke also holds that free agents must be able to introduce motion into the world (Works, 4:686).

69. The more general question of whether the laws of nature are necessary was discussed quite extensively in the eighteenth century; for a helpful overview, see André Charrak, Contingence et nécessité.

70. For a brief overview of Du Châtelet's metaphysics, see Karen Detlefsen, "Émilie du Châtelet," §4; Hagengruber, "Transformation." However, see also Marius Stan, "Emilie du Châtelet's Metaphysics of Substance," who argues that Du Châtelet's mature views are less Leibnizian than typically assumed and that she should be interpreted as a substance dualist.

72. Of course, large parts of the theory of freedom laid out in "On Freedom" are perfectly compatible with a monadological metaphysics—after all, the theory has deep similarities with Leibniz's own theory.

73. I thank two anonymous referees at the Journal of the History of Philosophy for enormously helpful and thorough feedback. Before reading their comments, I did not realize how fruitful it is to compare Du Châtelet's theory to Samuel Clarke's, to name just one example. Moreover, I thank Marcy Lascano for bringing "On Freedom" to my attention and sharing her work in progress on Du Châtelet with me; I also thank the participants of the 2017 Finnish-Hungarian Seminar in Early Modern Philosophy, the 2017 Atlantic Canada Seminar in Early Modern Philosophy, the modern philosophy workshop at Ohio State, and Anat Schechtman for extensive comments on earlier versions of this paper. Finally, I am grateful to Dai Heide for making me aware of the Cartesian discussions of occasional causation and to Karen Detlefsen for comments on a draft.

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