Johns Hopkins University Press

In QQ.23–31 of Olivi's Quaestiones in secundum librum Sententiarum (Summa II) and in Bacon's De multiplicatione specierum (DMS) 1.3, we find an intriguing discussion concerning the link between agent and patient in accounts of physical action in the Aristotelian tradition. Both thinkers hold that species were the link between agent and patient; they disagree, however, about the definition and function of species. The dispute leads the two thinkers to develop and clarify their accounts of physical action. They discuss temporality, secondary causality, active potentiality, and the distinction between virtual and substantial contact. This paper provides an account of Olivi's theory of species in medio and clarifies how it differs from Bacon's theory. It throws a spotlight on a significant episode in the history of philosophy, in which Aristotelian concepts were found unsuitable to account for action at a distance and in the interior of the patient, and hence new concepts of virtual action and species had to be devised.


Peter John Olivi, Roger Bacon, species in medio, virtual contact, physical action, active potentiality, force


did roger bacon and peter john olivi ever meet? We suggest a positive answer to this question. After he became a Franciscan in 1257, Roger Bacon (1214/12– 1292) spent ten years at the Franciscan Paris convent. In those years he wrote the De multiplicatione specierum (completed before 1266)—his most thought-out piece—the Opus majus, Opus minus, and Opus tertium, which he completed by early 1268. It is not clear whether Bacon returned to England after 1268, or [End Page 49] remained in Paris until 1280.1 Peter John Olivi (ca. 1248–1298) wrote the Summa questions (henceforth Summa II) in several phases.2 According to Sylvain Piron's chronology, Olivi's questions on Physics (QQ.23–31) should be dated before 1270, and his theory of will and vision (QQ.58, 72–74) after 1275.3 The earliest of Olivi's questions (some are still in mss.) deal with physical issues, as the young Olivi was probably teaching physics at the Fransciscan convent. Olivi entered the Franciscan order at the age of twelve, and studied in Paris from 1267 to about 1270. He spent the rest of his life teaching at various Franciscan houses of study in southern France. This chronology suggests the possibility that the two thinkers had been together at the Franciscan Paris convent in the years 1267–68, and perhaps even until 1272, as Bacon's whereabouts in those years is unknown.

A few scholars have entertained the possibility that the two thinkers knew each other personally, and were in fact engaged with each other's work. Katherine Tachau argues that Olivi arrived at the Paris convent while Roger Bacon and John Pecham (ca. 1230–1292) were resident there (Vision and Certitude, 39–40). We can be certain that Olivi studied at the Paris convent during 1267–1270, when Bacon was laboring over his Opus majus. When Olivi debated with the Perspectivists, Tachau claims, he was probably referring chiefly to Bacon (Vision and Certitude, 40). Tachau provides references to certain passages in Olivi in which he referred to specific Baconian ideas. Some more textual and thematical resemblances between Bacon and Olivi were found by Dominique Demange, who demonstrates Olivi's thorough knowledge of the optical works of Bacon and Pecham, which he must have learned as a young student in the Franciscan Studium in Paris.4 Ten lines of Q.58 of Olivi's Summa (II.492, ll. 2–12),5 we may add, were directly copied from Bacon's DMS 3.3 (114, ll. 139–46).6 And finally, in a recent paper, Hackett suggests that it is likely that Olivi was in fact Iuvenis Iohannes, a student mentioned in the Opus tertium with whom Bacon entrusted the crucial task of presenting his writings to the Pope.7

Bacon's influence on Olivi's theory of perception has been addressed in previous studies, and a debate has ensued regarding the question of the status of species in Olivi's philosophy. In Vision and Certitude, Tachau demonstrates that in the later questions of the Summa (QQ.58, and 72–74) dealing with the theory of vision, Olivi strongly objected to Bacon's theory of the multiplication of species. But was this also his position in the earlier questions (QQ.23–31), dealing with the physical theory of action? Robert Pasnau argues that, in the physical questions, [End Page 50] Olivi accepted the theory of the multiplication of species, though rejects it later on, within the frame of his theory of perception. According to Pasnau, Olivi accepts species of memory and allows that cognition based on memory and imagination may be explained by internal representations or species. On Pasnau's reading, Olivi does not reject species in medio, but merely denies that these species are the efficient cause of cognition.8 In support of his position, Pasnau quotes from Olivi's Epistola ad fratrem R., in which, after being accused of rejecting species, Olivi replied:

Sight so perceptibly verifies the multiplication of species in the case of rays of the sun and the shining out of illuminated colors that it is as if he who denies this needs punishment. And may God show mercy to those who attribute this [denial] to me, because I assert this everywhere. And in certain questions on the action of agents (which I composed too briefly and too obscurely), the multiplication of species is not only asserted but even presupposed as the subject of those questions.9

These lines are very puzzling. Olivi claims that he had asserted the existence and multiplication of species "everywhere," but in the Summa we can read long pages of harsh criticism of the theory of multiplication of species. Since the Epistola is dated April 22, 1283, that is, later than (or in the same years as) the questions on vision (QQ.58, 72–74),10 how can this assertion be compatible with his rejection of Bacon's multiplicatio specierum in these later questions? Two interpretations seem possible: either (Int1) Olivi changed his mind, accepting species at the time of the physical questions and rejecting them later on; or (Int2) Olivi granted the existence of physical species but denied them any psychological or cognitive role. Both interpretations, however, are inadequate.11 [End Page 51]

As we shall see, this difficult question becomes clearer once Olivi's account of the nature of physical species from his questions on Physics is introduced. If our understanding of these questions is correct, it appears that Olivi rejected Bacon's account of species from the beginning and proposed a different account, one more compatible with his own physics and psychology. The question is thus not whether Olivi accepted or rejected the existence of physical species, but rather, whether Olivi's account of the nature of physical species is the same as Bacon's.

Upon examining Olivi's theory of species as developed in QQ.23–31 of the Summa, it appears that Olivi was in discussion with Bacon. As we shall see, there is no doubt that the young Olivi was well aware of Bacon's theory of physical action ('Bacon's Theory,' henceforth, BT), as presented in the DMS. Moreover, in DMS 1.3, Bacon challenges an alternative theory ('Alternative Theory,' henceforth, AT) that is very similar to Olivi's theory of physical action, as found in his QQ.23–31 ('Olivi's Theory,' henceforth, OT). Whether Olivi can be formally identified as the main target of Bacon's attack is another question, which will be examined in section 4 of our study. But there is no doubt that the two philosophers are engaged with the same questions, using the same terminology, in the same place, and in the same years.

The following study contains four sections. In the first section, we give a short presentation of the question of physical action in the peripatetic tradition, which appears to be the background of Bacon's and Olivi's discussions. In the second section, we examine Bacon's theory of physical action (BT) in DMS 1.3 and the alternative theory (AT) he presented and criticized in these pages. In the third section, we consider Olivi's understanding of the concept of species and his theory of physical action (OT) in Summa II, QQ.23–31. Finally, in the fourth section, we discuss the results obtained and the possibility of identifying (OT) with (AT).

1. the source of the discussion between bacon and olivi

The point discussed by Roger Bacon and Peter of John Olivi has one of its major sources in Aristotle's account of generation of substances and properties in Metaphysics VII.7–9, 1032a–1035a and XII.3, 1069b–1070a, and in Averroes's comments on this point in his Long Commentary on Metaphysics, Book XII(,) tc.18.12 Both absolute generation (the change from non-substance to substance) and relative generation (the change from a privation of property to its possession) have the same principles: (1) a matter to be transformed (material cause), (2) a singular agent (efficient cause), and (3) the causational synonymy principle: everything is generated from its synonym:13 man begets man, an oak tree begets an oak tree, and fire begets fire. Aristotle aimed at demonstrating that Platonic forms are useless for the purpose of generation of substances or properties since a singular agent produces a singular effect of the same kind: no universal fire is needed for the generation of a singular fire, for this singular fire has been generated by another [End Page 52] singular fire. A problem remains concerning the spontaneous generation of some insects from putrescent matter or corpses, for which a singular efficient cause of the same form is lacking. Averroes considered this question as critical, because if it were possible to demonstrate that, even in the case of the most inferior being, generation is possible without a singular agent of the same form, then either (1) separate forms are causes of generation (Platonism) or (2) creation ex nihilo is possible, according to the opinion of the monotheist theologians (Mutakallimun). For in the first case (1), one of the targets of Averroes is Alfarabi's and Avicenna's theory of the giver of forms (dator formarum), according to which the universal Agent Intellect not only illumines souls to produce universal knowledge, but also generates the corresponding forms in concrete matter. Averroes identified this theory as Neoplatonic and rejected it as contrary to the principles of Aristotle's philosophy. More to the point, he considered that appealing to supernatural agents (an external transcendent God, or a dator formarum) for the purpose of explaining natural mechanisms destroys the principles of physical science. Moreover, while discussing Themistius's commentary, Averroes also rejected the possibility of preexisting germinal forms in matter, a theory whose source was the Stoic concept of seminal reasons (rationes seminales), which had become popular due to Augustine's transmission of it.

Bacon and Olivi discussed the question of the propagation of species in the medium and the production of physical effects in matter according to the Averroist scheme, appealing to no external supernatural agent, no giver of forms, no seminal reasons. Both considered nature as autonomous and searched for immanent causal mechanisms. Olivi devoted a long question (Summa II, Q.31) to refute Bonaventure's theory of seminal reasons, and Bacon criticized the idea of seminal reasons in the Communia naturalium (, 84–85).14 They described physical action as a process of generation, by a physical agent, of similitudes in the medium, or in the matter of the patient, without the help of supernatural agents and without any previous form existing in the matter of the patient.

Aristotle and Averroes claimed that the right model of physical action is to say that nothing of the effect is actually existing in the matter being acted on—nothing is present as an actual form or an already existing being of any kind—but that the form to be actualized is only present "in potency." This response was for Bacon and Olivi correct, but also insufficient and obscure, since a concrete model of physical eduction of this form is not given. By what mechanism is the agent producing its effect in the matter of the recipient? Is the agent introducing something from its own substance or power, or creating something completely new? Is matter in some way active in this process? How can the form be activated within an object, for example, how can an external fire cause heat in the interior of a piece of wood? Does this happen by propagation of some species, by introduction of a virtus, or by action at a distance? In the following sections, we consider how Bacon and Olivi addressed these questions. [End Page 53]

2. bacon's theory of physical action (bt) against an alternative theory (at)

The De multiplicatione specierum is the text in which Bacon provides the most elaborated and systematic account of his theory of the multiplication of species. In the first part of DMS, Bacon discusses the correct terminology and definition of the concept of species, including its properties (chapter 1); the various types of the agents producing species (chapter 2); and the agent's mode of action, namely, the physics of propagation, involving the agent, the medium, and the final recipient (chapter 3). At the beginning of the chapter 3, Bacon presents his own theory (BT [45–47]) and then refutes an alternative theory (AT [49]). Bacon presents this alternative as a "common theory" (decipit multos, multitudo), but it is not easy to find its sources, and the editor (Lindberg) does not identify them.

In DMS 1.3 (45–47), Bacon draws the following conclusions concerning the mode of action of natural agents:

(c1) "A species cannot exit from or be emitted by the agent itself"; "therefore, the vulgar express themselves badly and improperly when they say that an agent emits a species from itself."

(c2) "An agent does not create a species ex nihilo."

(c3) The agent does not "receive a species from outside itself and the recipient and deposit it in the recipient."

(c4) A species does not "come out into existence through an impression," in the narrow sense of an action on a surface ("the sort of impression made by a seal in wax"), because natural action occurs within the recipient.15

(c5) The way the species come into existence is "by bringing forth out of the potentiality of recipient matter," as Aristotle has demonstrated.

(c6) If we understand that species come into existence by the passive potentiality of matter, this leads to the error of the Dator formarum, which is contrary to the teaching of Aristotle. Therefore, species come into existence by being brought out of "the active potentiality of matter."

What is the "active potency of matter," according to Bacon? An extended explanation appears in the Communia naturalium. Many philosophers, Bacon remarks, understand Aristotle as saying that privation, namely, the appetite of matter to receive a form, is a principle of natural action. But that privation, Bacon argues, namely, matter's desire to be completed, is not a passive potency, but active (CN, 69). A passive potency, on Bacon's understanding, is the principle of corruption, which is a potency found everywhere in corruptible things. Therefore, the aforementioned privation is an active potency, by which matter desires its perfection (CN, 79). The active potency conditions the nature, perfection, and health of its substance. Bacon defines it as the essence of the material principle, and its potency as well. It is the essence as considered in itself, and it is potency considered as the appetite promoting and perfecting the substance (CN, 81–82). But placing an active potency within the recipient matter does not conform to Aristotle, who in Metaphysics IX locates the active potency in the agent, identifying the matter of the recipient with the passive potency. According to Dorothea Sharp, the recipient matter's potency considered as both active and [End Page 54] passive was not unique to Bacon. It appeared in Grosseteste, who maintained that potency is passive in the sense of being the subject of action, but active in reference to that which it is to become, namely, because it has some inner pre-adaptation to the forms that it is capable of receiving. In this way, Sharp argues, the impossibility of a transition from a pure potency to actuality is avoided.16 Grosseteste's assertion that potency does not mean that nothing is actual, but rather that not everything is actual, became one of the chief tenets of most Franciscan philosophers who refused to regard potency as a mysterious nothingness from which a new thing emerges.17 Bacon used the distinction between active and passive potencies in the same way as Grosseteste, arguing that matter's privation, namely, its desire for perfection, is active insofar as it desires a particular new form, and passive insofar as it is able to receive an indeterminate form.18 Anna Rodolfi considers that the notion of the active potentiality of matter enabled Bacon to dispense with form as the unique vehicle of being and reject the idea of a perfect identity between form and actuality.19 The active potency of matter makes it possible to speak of the actuality of matter that is not dependent on form. Unlike Sharp, Rodolfi argues that this is an original theory of Bacon's, not shared with other Franciscans, and that this position grants matter a sort of autonomy. This interpretation fits well with the remarks that we find scattered in Bacon's writing, that "matter is not nothing, but true nature and essence."20

At this point in DMS 1.3, we find the passage presenting AT:

But many are deceived by a certain objection to this. For it is argued that agent and recipient are joined to one another and there is no intermediary between them [Th1], as Aristotle proves in Physics, book VII, and determines in Metaphysics, book IX, and De generatione. For the principal condition of acting is that the agent and recipient must be conjoined without intermediary, for otherwise the former does not alter the latter. But conjunction can be understood in two ways, namely according to substance and according to virtue [secundum substantiam vel secundum virtutem] [Th2], as they say; but the agent cannot be joined to the interior of the recipient according to substance; therefore, it must be joined to it according to virtue, in such a way as to generate its effect by bringing it forth from the interior of the recipient [ut generet effectum suum per eductionem eius de profundo patientis] [Th3]. Consequently, the multitude says that this is the giving and infusing of virtue into the interiorthe agent and the virtue to be generated, and of the recipient, in order to bring forth the effect out of its potentiality [ut de potentia eius educatur effectus], and that the virtue [itself] must not be generated out of that potentiality. And therefore it is supposed that virtue or species is not brought forth out of the potentiality of matter [ponitur quod virtus seu species non educitur de potentia materiae] [Th4], but that it is given and infused and that it is different from the effect finally intended [ab effectu intento finaliter] [Th5]; and it is produced only by the agent [Th6], in order to alter the interior of the recipient, and through it the effect is brought forth out of the potentiality of the matter. Thus it is the instrument of the agent [instrumentum est agentis] for producing its principal effect. And they say that in no other way could an agent produce its intended effect, as fire produces fire or the form or fire; nor [End Page 55] could man produce man; nor could any agent produce an effect similar to itself in name and definition

(Bacon, DMS 1.3 [49]).

For Bacon, a species, once issued, is independent of its agent, and can continue to exist after its agent has perished. Once the first species is produced, further species, similar to the first one, are on their way: "a species, once it has been multiplied in the medium, requires only the medium; and by itself, from its active power, it can produce its like" (Bacon, DMS 3.1 [185]). Once issued, a species becomes not only independent of its source, but also a secondary cause, producing other species. Bacon thinks of these species as identical in essence and operation, yet as numerically and locally different. For AT, by contrast, there is no intermediary between the agent and the patient (Th1). AT takes for granted the Aristotelian principle of union between agent and patient in the same act, as demonstrated at length in Physics VII. 2 (243a3–245b1): there is no medium between the mover and the moved. Aristotle's theory of action has no need of species in medio, and therefore AT concludes that they have to be eliminated, "for the principal condition of acting is that the agent and recipient must be conjoined without intermediary, for otherwise the former does not alter the latter" (DMS 1.3 [49]).

But without the multiplication of species, how is action at a distance possible? This is a problem Aristotle did not solve.21 Medieval philosophers thought that action at a distance (especially the action of the planets and the stars on earth) could be explained by a specific mode of contact: the contact of power (secundum virtutem). Thus, for AT, there are two possibilities of contact (Th2): according to substance (secundum substantiam) or according to virtue (secundum virtutem). This distinction can be found in Aquinas,22 Olivi,23 Richard Rufus,24 and later in [End Page 56] John Duns Scotus.25 Bacon also alludes to it in other passages.26 Whereas "contact according to substance" or "mathematical contact" is the classical (Aristotelian) surface contact, "contact according to power" (tactus virtualis) allows direct action of an agent upon a distant object.

According to AT, a virtue or species is directly infused into the patient by the power or first effect (taken as an instrument) of the agent ("this is the giving and infusing of virtue into the interior of the recipient" [DMS 1.3 (49)]). This virtus or species is introduced by the agent in the interior of the patient so as to move it at a distance (Th3). Moreover, this virtue has not been brought forth from the matter of the patient but emitted by the agent alone (Th4, Th6): "and that virtue itself must not be generated out of that potentiality [of matter]" (DMS 1.3 [49]). Last, but not least, this virtue is really different from the final effect of the action (Th5): the agent creates in the passive matter a force that has instrumentally the function of moving the patient toward the goal (the intended effect). This introduction of virtue or species is not the final effect of the action, but the instrument of this final effect ("Thus it is the instrument of the agent for producing its principal effect" [DMS 1.3 (49)]).

Let us now consider Bacon's response to AT. Aristotle said that agent and patient are in immediate contact, and Bacon agrees: in natural action, the active substance of the agent touches the recipient's body with its physical body, which has three dimensions (however small). According to Bacon, the very principle of physical action by the propagation of species renders AT's distinction between substantial and virtual action redundant:

the agent need not be in the interior of the recipient according to its substance or in any other way, in order for something to be brought forth out of the potentiality of the interior, because natural action does not require this. Nor does Aristotle so determine, but only that between agent and recipient there is no intermediary; for thus the active substance of the agent, touching the substance of the recipient without intermediary, can alter, by its active virtue and power, the first part of the recipient that it touches. And this action flows into the interior of that part, since the part is not a surface, but a body, however small it may be; nor can it be perceived or understood without its depth—and therefore without depth it can be neither touched nor altered. . . . For since the agent touches the recipient, and not only the bare surface, but the substance [of the recipient] through the mediation of the surface (and this substance is body, however small it may be, and therefore possesses depth), I say that the agent sufficiently touches the interior of the first part. And it is unnecessary for it to be in that interior, either according to substance or in any other way

(Bacon, DMS 1.3 [53]).

Bacon thinks that each agent strives to render its surroundings similar to itself. He therefore holds that the final effect is no different than the first effect, which is a similitude of the agent, namely, the species. He objects to AT's two-step process [End Page 57] (Th5), presenting three arguments:

  1. (1). Those who claim that the agent cannot act on the interior of the recipient, pose a third entity between the agent and the final effect. This third entity is the virtue, which is not the same as the final effect (Th5). So they posit the substance of the agent and its virtue as two separate entities, and the recipient as a third entity. But this would lead to an infinite regression, whereas a fourth entity would have to be placed between the agent and the virtue to be generated, and so on (DMS 1.3 [51]).

  2. (2). When fire transmits heat to a piece of wood, the fire impresses in it the species of heat, and this species becomes the accidental form of wood. The form of the agent (the form of fire) does not alter its own matter (the matter of fire): no form alters its own matter, except in the case of living bodies, for which the form is a soul which can act on the body as a motor. But in our case, the form of fire does not alter its own matter; it rather alters the air immediate to it, producing in it a species of heat which multiply from it into the piece of wood. When the species is transmitted to the first part of the wood, it cannot produce any other effect on the matter of this part; it can only make the same alteration in the first part, second part and so on (DMS 1.3 [51]).

  3. (3). Bacon challenges his opponents to explain where the original virtue goes to after it had made the first effect: if it corrupts into nothingness, then it can also be created from nothingness, and this is absurd (DMS 1.3 [50]).

Finally, Bacon rules out the possibility that a natural agent would create a form in the patient from nothing (see c2 above) and hence declares that the agent stirs the patient into generating this virtue from itself. The main argument against (Th4) and (Th5) is that physical action according to AT would be a creation ex nihilo, and "an agent does not create a species ex nihilo" (c2, DMS 1.3 [45]). On the contrary, BT holds (as we have seen) that the species is brought forth from the active potentiality of the patient's matter (c6).

3. olivi's account of physical species and his theory of physical action in summa ii qq.23–31 (ot)

The difficulty raised by Tachau's and Pasnau's contradictory interpretations requires a clear account of Olivi's concept of species and his theory of physical action by means of species. On these points, Olivi is directly referring to Bacon's theory, which was well known in the Franciscan milieu in the 1260s.

Bacon opens his treatise De multiplicatione specierum with a list of different expressions, which in his opinion are being used for one and the same thing, namely, species:

[it] is called 'similitude' and 'image' with respect to the thing generating it, to which it is similar and which it imitates. It is called 'species' with respect to sense and intellect, according to the use of Aristotle and the naturalists. . . . It is called 'idol' with respect to mirrors. . . . It is called 'phantasm' and 'simulacrum' in the apparitions of dreams, since these species penetrate sense as far as the interior parts of the soul. . . . It is called 'form' by Alhazen. . . . It is called 'intention' by the multitude of naturalists because of the weakness of its being in comparison to that of the thing itself. . . . It is called 'shadow of the philosophers,' since it is not clearly sensible. . . . It is called 'virtue' with respect to generation and corruption. . . . It is called 'impression' because it resembles impressions. . . . It is called 'passion' because the medium and sense, in receiving species, undergo a transmutation in their substance

(DMS 1.1 [5]).

[End Page 58]

This is both an ontological and a terminological statement, which attempts to establish a unified philosophical vocabulary. Species becomes in Bacon's system a general concept, covering several ideas of various origins that, in his view, are in fact partial aspects of one and the same thing. Bacon's strict definition of species is given on the next page: it is "the first effect of any natural agent" (DSM 1.1 [7]). As its first effect, a species resembles its agent in "nature, specific essence and operation" (DSM 1.1 [7]). A species, according to Bacon, must belong to the same category and be of the same genus as its agent. Thus, the species of a substance is substance, the species of an accident is accident, the species of a composite is composite, the species of a form is form, and the species of matter is matter (DMS 1.2 [43]). Since Bacon declares that all natural changes are produced via species, this similarity between the agent and its species could be considered a tribute to Aristotle's causal synonymy principle. What, then, is the difference between the agent and its species? The only difference is that the being of the agent is complete, whereas the being of its species is not (DMS 1.1 [11]). Indeed, since its being is "exceedingly incomplete," a species does not have dimensions of its own and so must partake of the dimensions of whatever medium it is in (DMS 3.1 [181]). Thus, a species "does not occupy space through itself, but through something else" (DMS 3.1 [183]). The passage of species through the medium is not a movement but involves its multiplication in straight lines, or successive generation in the consecutive parts of the medium. Each species begets the next in line in a process of true physical change, while taking on the matter of the medium. The process of multiplication continues within the recipient, where the species takes on the matter of the patient and transforms it to produce the final effect, rendering the patient similar to the agent.

For his part, Olivi provides the following definition of species: "Whatever is made from the agent without being educed from the potency of matter, appears as an influx from the agent and of the genus of the first impressions which first emanate from agents."27 He stresses that "The emanating species draws its whole essence directly and immediately from its proper and immediate influent, so that its influent is the radical and original basis of the emanating species."28

What is a species, then? It seems that Bacon and Olivi agree that it is the first effect of a natural agent, namely, the first thing emitted by an agent, the first "impression" of this agent, having the source in its very essence. Both thinkers explain physical action in terms of the production of a similitude. So if Bacon and Olivi agree that every natural agent produces a species or similitude, where is the problem?

In Q.24, Olivi addresses the following issue: "Whether a species or a similitude of the agent, which is said to be its impression, is educed from the potency of matter or the patient, or is it made only by a simple emanation of the agent."29 By [End Page 59] what mechanism is a species transferred from agent to patient, and how is matter implied in this process? The first position presented in this question is without any doubt Bacon's:

To this question, some want to say that every impression of agents and universally, everything that is made by a created agent, is educed from the potency of matter, relying on the aforementioned reasons. According to their position, they allege to say that species of colours and luminous [objects] truly mix in the medium by a natural mixture, in such a way that their first qualities are blended in the mixture, and that they educe from the potency of the medium all the substantial forms of celestial bodies, minerals, and animate bodies similar to the medium, so that in the air is given something of the truth of all forms that can impress their species on it, yet not completely, and this is only because of the deficiency of the patient [the medium].30

According to this theory, every natural agent produces, by its very substantial form, a similitude in the matter affected by its action; this species or similitude is brought forth (educitur) from the potency of the matter of the patient. Since the medium is also affected by such a process, and since (according to Bacon) the species of material things have material and corporeal being in the medium, the species of all natural things must really mix in the medium. Another argument in favor of this theory relies on the principle of similarity in name, definition, and essence between agent and species: if the things generating the species are compounded when they are in the same subject, so must their species be compounded when they are in the same medium. Bacon discusses this theory in DMS 3.3 (195), stating, "I say absolutely that the species of corporeal things are mixed in every part of the medium." Bacon's theory of the real mixing of species in the medium was rejected by most philosophers in the thirteenth century in favor of Averroes's theory, which grants species only spiritual being. However, Bacon also holds that the being of the species in the medium is deficient, since the medium is not the matter in which the species can best express their content, according to his theory of "incorporation." 31

Immediately after presenting it, Olivi replies to Bacon's theory of physical action (Q.24, 435–36), adducing four arguments against it: [End Page 60]

  1. (1). Species is the first effect emitted by the agent; hence, it cannot be brought forth from the matter of the patient. The patient cannot be moved to a new form or state without receiving an impulse (impulsus) or inclination (inclinatio) directly from the agent. For instance, the stone that is thrown away receives an impulse or push from the agent, the effect being a change of place. This movement cannot be caused by another movement, for it would lead to an infinite regress. Thus, the impulse at the very origin of the movement is immediately produced by the agent, rather than being 'brought forth' from the matter of the patient: "Since therefore the impressions of the agent are those that are made first by the agent on the patient and by which it is moved towards the form, it is necessary that they not be educed from the potency of matter."32

  2. (2). The first and immediate action of the agent is different from the form educed (forma educta) in the matter of the patient. Demonstration: some forms naturally produced are still present in the patient when the agent is no longer present, so the previous action of the agent implies something other than the form produced ("the action which the agent produced then was different from the being of educed form itself [actio quam tunc faciebat agens erat aliud quam esse ipsius formae eductae]," Summa II, Q.24 [I.436]). This is clear, since the form is produced by a movement, and the movement implies a change from a form to its contrary (e.g. from cold to hot). The first action of the mover is also a case of instantaneous contact (in instanti), not movement: "therefore, everything that does not have a contrary in the matter in which it is produced, is made in some other way than by being educed from the potency of matter."33 This point can be illustrated by an argument found in Q.29: one can transmit an impulse to a heavy stone without having any effect on it, for example, when one pushes on it without producing any local motion. So the action of the agent (the impulse) is one thing; the effect of the action on the patient (the form induced in the matter of the patient) another.34

  3. (3). The form produced in the matter of the patient does not depend on the agent for its permanence, that is, it can remain in existence when its agent ceases to exist. The first action of the agent, however, exists only when the agent acts ("the first impressions of agents do not remain, nor can they remain, except during the time when the agent acts [impressiones primae agentium non manent nec manere possunt nisi quamdiu agens agit]") (Summa II, Q.24 [I.436]).

  4. (4). The first impressions of agents cannot be brought forth from the potency of the matter of the patient because if they were, the destruction of these first impressions would require a change in the matter of the patient, which must be caused by the action of a contrary agent. However, in many cases those impressions are destroyed without any action by a contrary agent (Summa II, Q.24 [I.436–37]). A cold stone, for example, cannot become hot without the action of a warming agent and a hot stone cannot become cold without the action of a cooling agent. The Aristotelian tradition describes these contrary movements as changes from one contrary state to another, caused by an active agent. But experience teaches that the light of a candle, for example, disappears immediately when the candle is blown out; this suppression [End Page 61] of the first impression (light) of the agent (the candle) does not result from a contrary agent, but simply from the end of the action. Therefore, no opposite change in the matter of the patient occurred, which implies that the matter of the patient did not undergo a physical change. (Summa II, Q.24 [I, 436–37])35

Lastly, Olivi rejects Bacon's idea of the physical mixture of species in medio, arguing that it is not immediately relevant to the question at stake:

What they say, however, concerning mixtures, does not seem in any way to be true, also according to the others [philosophers], and even less when they say that in the air there is something of the nature of all corporeal forms educed from its potency. Because it is not entirely relevant to the subject matter of the present question, I will pass over for now.36

The way Olivi uses the terms actio, species, impressio, inclinatio, similitudo, and impulsus in QQ.23–29 is quite unusual. (A1) According to the classical (Baconian) definition above, Olivi equates species with impression and similitude ("the species or similitude of the agent, which is called its impression [species seu similitudo agentis quae ipsius impressio dicitur]"). (A2) Action is the same thing as the species produced ("action is not the cause of species, since they are the same [actio non est causa speciei, cum sint idem]") (Summa II, Q.25 [I.443]). The reason is that, according to Aristotle, "acting" (agere) and "being affected" (pati) are the same thing, considered on the side of the agent or the patient. We cannot speak of "action" if nothing is produced and the effect produced is the action itself.37 (A3) This action-species is not the same as the form actualized in the matter of the patient. The main thesis of Q.24 is that the species or similitude of the agent (its impression) is a different thing than the form that is educed from the potency of the matter by movement. (A4) The terms impulsus, inclinatio, and impetus have the same meaning.38 An impulse or inclination is not a movement but its cause.39 Olivi holds that form cannot be produced in passive matter without an impulse [End Page 62] or inclination that is logically prior to and different from the form produced.40 In order to produce a form in the matter of the patient, the agent has first to cause an inclination in the matter. (A5) The first impulsion or inclination produced by the agent is instantaneous, emitted immediately by the agent alone.41 (A6) Movement is defined as the progressive response of the matter of the patient to the agent's impulsion, leading to the final form:42

In the first virtual contact between the mover and the moved, or the agent and patient, the moveable is affected by the mover. But it is clear that their first contact occurs in an instant; therefore the quality produced in a moveable thing by the mover at their first contact happens in the first instant of this contact, and so the contact naturally precedes the inchoate movement initiated in that instant, and cannot potentially be produced or exist in it.43

So the core of Olivi's theory (OT) appears to be the following: (1) the agent causes an impulse or inclination in the matter of the patient by virtual contact (tactus virtualis); (2) this first contact is instantaneous; and (3) the matter's response to this impulse is a movement, by which a form is finally acquired.44

This unusual way of considering the concept of species and the way species are produced indicates that Olivi is not following Bacon. The instantaneous nature of the first contact, for instance, contradicts Bacon's theory of action, in which the multiplication of species is always temporal. In Q.26, Olivi asks whether the first impressions of agents are immediate and the answer is affirmative. Olivi alludes to Alhacen as his source for the opposing view: according to the Perspectivists, all impressions need time, although this time is for us imperceptible.45 Most medieval thinkers did not consider generation and corruption to be kinds of motion, but rather mutations, or instantaneous changes, whereas other varieties of change were viewed as gradual and successive processes.46 The spread of light was a case of mutation. Aristotle and his followers believed that since it is a quality acquired by the medium all at once, light has no speed. Olivi is in agreement with this view. The exception was Alhacen, who held that light travels at a finite, [End Page 63] though imperceptible, speed.47 Bacon follows Alhacen. In fact, he considers the multiplication of species to be a case of generation rather than mutation, whereas Olivi considers the first action of all agents (and so the first emission of light) to be a mutation. According to Bacon, generation, like all other natural processes, occurs in time. The transmission of light through the air or any other transparent medium is a real generation of species using the matter of the air, and must be a successive or temporal process: "Therefore the motion of a species according to prior and posterior [parts] of space entails priority and posteriority in duration, and thus in time" (DMS 4.3 [23]).48

By contrast, Olivi holds that the transmission of species in the air is instantaneous, since the matter of the air is not transformed in this case. When the sun shines on a stone, there are three physical processes involved: (1) the instantaneous emission of light (its action or species) by the sun; (2) the instantaneous transmission of light through the air; (3) the gradual warming of the illuminated stone. Processes (2) and (3) are different, for in (2) the air has the sole function of a medium simply transmitting the species, whereas in (3) the stone is the subject of the movement by which its matter is transformed.49 The sun itself is in immediate contact with all points in the area of it illuminates.50 Following Augustine, Olivi holds that the effects of illumination in the medium are not to be considered successive in the temporal sense, but only according to their natural order from the source (Summa II, Q.26 [I.452]). The heat of the sun is immediately infused into the interior of the stone, and the matter of the stone slowly responds to this action by actualizing a new state of heat.

4. at and ot considered

QQ.23–26 provide a complex description of Olivi's concept of species (similitudo, impressio, etc.) and of his account of the process of their physical action. Olivi narrows down the significance of species to immediate contact between the agent and the patient, rejecting the Baconian principle of the multiplication and propagation of species as entities distinct from the agent's action. According to Olivi, the effect is "immediate" in the sense that there are intermediate effects in the medium but no intermediate causes.51 For instance, all the points of the sun's rays are immediately emanated by the sun and do not generate one another; there [End Page 64] are intermediary effects but not causes, just as one would not say that the drops in a stream of water generate each other. Consequently, the question raised by Pasnau (see our introduction) about Olivi's defense of the multiplicatio specierum in the Epistula ad fratrem R. seems to have the following solution. Olivi accepts the existence of species as effects of natural agents: the sun illuminates this wall, this flower, and this stone, so we have three species of the sun's light. But the sun (the first agent) is their only cause and the species do not generate others in the medium. Olivi rejects the idea of species as secondary causes, generating each other, because that would deprive the primary agent of its power.52 He rejects what he considers the "pagan" scheme of the Liber de causis, in which secondary causes can act independently of their source.53 Species are therefore pure effects. They cannot act by themselves, and this is Olivi's main point of contention. Accordingly, in the Epistola, Olivi could have taken for granted the existence of multiplicatio specierum without explaining that this multiplication was not a generation of successive causes.

Against Bacon's model, according to which species within a patient are produced by the agent not immediately but by being successively multiplied from the point of surface contact between the agent and patient (Summa II, Q.23 [I.423]), Olivi contends that positing the multiplication of species as separate entities would give rise to an actual infinity of separated beings in the medium. Since physical multiplication implies real separation between the successive generated elements, no mathematical continuity of the medium can be obtained by physical multiplication without generating infinitely many separated species (Summa II, Q.23 [I.426]). The argument is developed at length in Q.23 (I.426–27) through mathematical analysis of the process of generation. The generation of new species requires a continuous medium but also continuity of the species itself. Olivi views Bacon's conception of species as simple and dimensionless, and a simple and dimensionless species cannot generate a new species because physical generation requires surface contact between the generans and the generatum. If species were dimensionless, they would have no surfaces to be in contact with, and so generation would be impossible. If, however, species have corporeal extension, they would be both internally continuous and continuously generating each other in the medium, which is the same as saying that there is a unique continuous generation.

On the one hand, Bacon rules out the possibility that a natural agent could generate a form in the patient from nothing (see c2 above) and accordingly declares that the agent stirs the patient into generating such a form or species from itself. Olivi, on the other hand, holds that the agent does indeed generate a species in the patient ex nihilo, but he introduces a distinction between absolute creation, based on absolute power, and relative creation, in which finite agents [End Page 65] need a terminative cause to exert their power (Summa II, Q.31 [I.551–52]).54 His reasons for holding to this position are mainly theological: since no one would want to argue that the form of sin somehow exists in the sinner before he sins, it must be created in the soul as a new form. Thus, no one should have a problem with the idea that agents in general can create new forms in matter, which is why Olivi introduces some distinctions in order to support the idea that physical action, while not the same as creation in an absolute sense (which is proper only to God), is still ex nihilo.55

Considering now the relations between AT and OT, we cannot but conclude that there are strong similarities. (Th1) to (Th6) fit well with the theory of physical action in Olivi's Summa. (Th1) is Olivi's response in Q.23 ("whether every agent is always present to its patient or its first effect [an omne agens sit semper praesens suo patienti seu suo effectui primo]"). The distinction between substantial and virtual contact (Th2) and the application of virtual contact to physical action "in the interior of the patient" (Th3) is found in the same question. There is also a real distinction between the virtue as the first emanation of the agent (Th6), which is emitted by the agent alone (Th4), and the final effect educed from the potentiality of the matter (Th5), in Q.24, ("whether the species or similitude of the agent, which is called its impression, is educed from the potentcy of the matter or the patient or produced only by simple influx of the agent [an species seu similitudo agentis quae ipsius impressio dicitur educatur de potentia materiae seu patientis vel fiat solum per simplicem influxum agentis]"), and Q.25 ("whether the species or similitude of the agent is the same as its action [an species seu similitudo agentis sit idem quod eius actio]"). So can we conclude that Bacon is in fact attacking Olivi's theory in DMS 1.3?

The main textual argument against identifying AT with OT is that Bacon presents AT as the position held by "many" (decipit multos, multitudo). But which philosophers were those? As we have seen, AT appears as a way of dealing with the problem of action at a distance in the scope of Aristotelian physics, in the course of rejecting the theory of Alkindi and Grosseteste of the radiation of power through a mathematical representation of physical action by oriented forces, angles, and multiplication. In other words, AT represents Parisian innovation in Aristotelian physics distinct from, and perhaps even opposed to, the physics developed at Oxford by Grosseteste and his followers. There are thus good reasons to consider OT as a good example of Parisian physics in the 1260s, confirming Piron's suggestion that the young Olivi learned and subsequently taught physics at the Paris Franciscan convent in Paris. Nevertheless, it seems difficult to imagine that Bacon was addressing Olivi's physical questions QQ.23–31 in DMS 1.3 since [End Page 66] QQ.23–31 refer to BT in a way that indicates Olivi had good knowledge of the DMS—unless Olivi's first knowledge of BT came from earlier sources, such as the first book of the Communia naturalium. No definite conclusion can be drawn here, for there are too many uncertainties concerning the dates of the texts, which were revised by Bacon and/or Olivi at various periods. Finally, it must be said that relations between texts is one thing, personal relations between scholars another. When he composed DMS 1.3, Bacon may have had foremost in his mind some in-class debates or informal discussions on physical questions with a young scholar in the Franciscan convent.


We have shown that in QQ.23–26 of the Summa and in DMS 1.3, Olivi and Bacon are engaged in a discussion of the characteristics and function of species in physical action, as a part of their efforts to fill in the gaps in the Aristotelian account. We identified two main points of contention, namely, the ontological status of species as an entity independent of its agent or as an inseparable property of its agent, and the way in which a species is related to matter in physical processes: is the species educed from the potentiality of the matter of the patient, or is it an "external" force that merely sustains matter without informing it? The dispute over these two main points leads the two thinkers to develop and clarify their accounts of physical action. They discuss whether a distinction between virtual and substantial contact needs to be posited in order to account for action at a distance and in the interior of the patient; whether all physical processes happen in time or instantaneously, a distinction that was used to clarify the concepts of motion, mutation, and generation; and to what extent the introduction of a new form into matter can be compared with ex nihilo creation. This discussion was a significant episode in the history of physics and philosophy, in which Aristotelian analysis was found unsuitable to account for action at a distance and hence new concepts such as virtual action and species had to be devised.56 [End Page 67]

Dominique Demange

Dominique Demange is professor ('conferences master') of ancient and medieval philosophy at the University of Paris-Nanterre

Yael Kedar

Yael Kedar is lecturer in philosophy at Tel Hai College and a research fellow at the University of Haifa.

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1. See Stewart Easton, Roger Bacon, 187; and Jeremiah Hackett, "Roger Bacon."

2. Despite the title given by the editor, Bernard Jansen, these disputed questions are not from a commentary of the Sentences, but from a theological Summa. See Victorin Doucet, "De operibus"; and Sylvain Piron, "Les oeuvres."

3. See Piron, "Parcours," "The Formation," and "Le métier."

4. Demange, "Olivi et les Perspectivi."

5. References to this work are according to questions. The volume and page numbers (and, where relevant, the line numbers) in Bernardus Jansen's edition, published by Collegium S. Bonaventurae, are in brackets.

6. References to this work are by section number, with page numbers (and, where relevant, line numbers) in brackets from David C. Lindberg's translation.

7. Hackett, "Roger Bacon."

8. See Pasnau, Theories of Cognition, 168–69. According to Pasnau, "Olivi's criticisms of the species theory, like Ockham's, cover a particular class of cognitions, roughly, the kind that Ockham would call intuitive. Olivi accepts memory species and habits, and in general he allows (as Ockham does) that cognition based on memory and imagination may be explained by internal representations or species. Olivi does not even reject species in medio, and here of course he is differing from Ockham. But Olivi denies that these species are the efficient cause of cognition."

9. Olivi, Epistola, 33–64; art.13, 55–56; cf. Pasnau, Theories of Cognition, 169n24. This translation is by Pasnau. On the historical origin of this letter, see the introduction to the edition of Olivi's Epistola, 33–45. Olivi is accused of the following proposition: "Quod res non multiplicant species suas sed ab anima per essentiam cognoscuntur." The first part of his response is the following: "Multiplicationes specierum in solis radiis et in refulgentia colorum irradiatorum visus ita sensibiliter comprobat, quod quasi poena indiget qui hoc negat, et parcat Deus illis qui hoc mihi imposuerunt, cum ego hoc ubique asseram, et in quibusdam quaestionibus quas de actione agentis nimis breviter nimisque obscure conscripsi non solum asseritur multiplicatio specierum: sed etiam presupponitur quasi subiectum quaestionum ipsarum."

10. Piron, "Censures."

11. (Int1) is formulated by Piron (see Epistola, 55art.13) and (Int2) is Pasnau's. (Int1) is impossible if we believe Olivi when he writes that he "asserted the existence of species everywhere." About (Int2), it is not so clear that accepting the existence of species for the purpose of analyzing physical phenomena such as illumination is compatible with the rejection of species as the psychological cause of vision. If light or color produces its own species in the medium and the aspectus emitted by the eye (according to Olivi's theory) is able to see the air illuminated, would this not mean that the aspectus will see the physical species emitted by the sun in the air? But this is precisely what Olivi rejects in QQ.72–74, because according to him, we do not see the species in medio (Summa II, Q.73 [III.84]): "noster visus videt totum spatium intermedium inter se et obiectum. Quare ergo non videbit species existentes in illo spatio, et maxime cum ipsum ut per eas informatum debeat esse visibilius quam sit ex se solo?" Moreover, in QQ.72–74, some arguments against the multiplicatio specierum have their source in the physical questions QQ.23–31, e.g. the consequence of the infinity of species in the medium, and thus the impossibility of their concrete physical generation (cf. Q.73 [III.76–77] and Q.23 [I.425–26]).

12. Genequand, Ibn Rushd's Metaphysics, 105–12.

13. Helen Lang, The Order, 71, calls this the "suchlike principle," according to which the actuality of the mover and the potentiality of the thing moved must be the same.

14. Seminal reasons, according to Bacon, are no more than the active potencies of matter. References to this work are according to book, part, distinction, and chapter in Robert Steele's edition published by Oxford.

15. Bacon, DMS 1.2 (45–47).

16. Sharp, Franciscan Philosophy, 122–23.

17. Sharp, Franciscan Philosophy, 15.

18. Sharp, Franciscan Philosophy, 122.

19. Rodolfi, "Dicitur materia," 90–92.

20. Bacon, Compendium studii theologiae, part 2, ch. 3, para. 80: "Materia enim non nihil est, sed vera natura et essentia."

21. On action at a distance and virtual contact in the Middle Ages, see the studies of Francis Kovach, "The Enduring Question"; and Nicolas Weill-Parot, "Le contact," "Pouvoirs lointains," Points aveugles, "Innovation," and especially "Le contact virtuel".

22. Aquinas, Summa Theologiae I, Q.105, art. 2 ad1m (Leonine Edition, T.5, 1889, 472b): "Ad primum ergo dicendum quod duplex est tactus: scilicet corporalis, sicut duo corpora se tangunt; et virtualis, sicut dicitur quod contristans tangit contristatum"; Summa contra gentiles II, ch. 56 (Leonine Edition, T.13, 1918, 403b): "Hic autem tactus non est quantitatis sed virtutis. Unde differt hic tactus a tactu corporeo in tribus. Primo quidem, quia hoc tactu id quod est indivisibile potest tangere divisibile. . . . Secundo, quia tactus quantitatis est solum secundum ultima, tactus autem virtutis est ad totum quod tangitur. . . . Ex quo patet tertia differentia. Quia in tactu quantitatis, qui fit secundum extrema, oportet esse tangens extrinsecum ei quod tangitur. . . . Tactus autem virtutis . . . cum sit ad intima, facit substantiam tangentem esse intra id quod tangitur." These three characteristics of virtual contact according to the Summa contra gentiles fit well with Olivi's account of virtual action.

23. Olivi, Summa II, Q.23 (I.429–30): "tactus enim mathematicus seu superficialis non est causa actionis et passionis, alias caelum pateretur ab igne, sed tactus naturalis seu virtualis: videtur igitur istis necessario ponendum quod virtus agentis attingat virtualiter in profundum patientis, quamvis ibi non sit substantialiter seu secundum suam substantiam, hoc est, quod sit praesens in ratione agentis seu agere et movere potentis et non in ratione coexistentis; quod non est aliud secundum istos nisi quod virtus est ita efficaciter inclinata in partem longinquam patientis quod immediate potest ab ea impressio sequi, ita quod immediatio excludat causam aliam intermediam, sed tamen non effectum intermedium." See also Summa II, Q.23 (I.430): "videtur igitur istis necessario ponendum quod virtus agentis attingat virtualiter in profundum patientis, quamvis ibi non sit substantialiter seu secundum suam substantiam, hoc est, quod sit praesens in ratione agentis seu agere et movere potentis et non in ratione coexistentis."

24. Richard Rufus of Cornwall, In Aristotelis De generatione et corruptione, Book I, ch. 5, 152: "Agens aut tangit naturaliter aut mathematice. Si mathematice, ergo solum agit secundum superficiem; si naturaliter, ergo influit virtutem suam in patiens."

25. John Duns Scotus, Quaestiones, VIII, Q.3, 446–47: "Tactus mathematicus non est necessarius agentis et patientis. Cum enim non tandant nisi secundum superficies ultimas, non agunt nisi in illas, et illa in aliam. . . . Igitur requiritur tactus virtualis, et sic intelligitur Aristoteles, VII Physicorum, 'praesens in ratione potentis agere'; et sic est praesens profundo passi, ubi non est eius essentia."

26. Bacon, De generatione et corruptione (Quaestio "Dubitatur utrum tangant secundum istam particulam,'agentibus'"): "duplex est tactus, aut secundum virtutem solum aut secundum virtutem et superfi-ciem."

27. Summa II, Q.27 (I.471–72): "Quicquid etiam fit ab agente absque hoc quod educatur de potentia materiae videtur esse influxus agentis et de genere primarum impressionum quae primo manant ab agentibus."

28. Summa II, Q.72 (III.20): "Species influxa trahit directe et immediate totam suam essentiam a suo proprio et immediato influente, ita quod suum influens est radicalis et originalis basis speciei influxae."

29. Summa II, Q.24 (I.434): "An species seu similitudo agentis quae ipsius impressio dicitur educatur de potentia materiae seu patientis vel fiat solum per simplicem influxum agentis."

30. Summa II, Q.24 (I.434–35): "Ad quaestionem istam quidam dicere voluerunt quod omnis impressio agentium et universaliter omne quod fit per agens creatum educitur de potentia materiae innitentes praemissae rationi. In tantumque positionem suam praetenderunt quod dixerunt species colorum et luminum vere in medio misceri mixtione naturali, quemadmodum in mixto miscentur primae qualitates, et quod omnes formae substantiales corporum caelestium, mineralium et corporum animatorum educunt de potentia medii sibi similes, ita quod in aere est dare aliquid de veritate omnium formarum quae speciem suam in eo imprimere possunt, non tamen complete, et hoc non est nisi propter defectum patientis."

31. According to the principle of incorporation, all objects express their nature through their species, but when those species exist outside their generating object, they must be incorporated in some manner. What a species actually expresses depends on what it is incorporated with. Within the transparent medium, for instance, a species expresses only the colored luminosity of the object's surface; when incorporated within the crystalline lens, it expresses the visibility of that surface; and when it is in the anterior cell of the brain, the object's perceptibility is expressed. Thus, every species incorporates the full range of its object's attributes and has the power at any time to express that range. Yet this power can only be realized if the species is incorporated within something that can actually bring it out, and each sort of matter is capable of bringing out only a few of its potential expressions. See Mark Smith, Alhacen's Theory, lxxxviii.

32. Summa II, Q.24 (I.435): "Cum igitur impressiones agentium sint illud quod primo fit ab agente in patiens et per quod movetur ad formam: necesse est quod non sint eductae de potentia materiae."

33. Summa II, Q.24 (I.436): "omnia igitur quae contrarium non habent in materia in qua fiunt, fiunt aliter quam per eductionem de potentia materiae."

34. Summa II, Q.29 (I.500–501): "ex experimento quod videmus in proiectis et in omnibus iis quae a nobis vel ab aliis moventur per impulsum; videmus enim in istis quod primo impelluntur et inclinantur ad certum terminum loci, antequam localiter moveantur; unde et contingit quod aliquando impelluntur, et tamen motus localis non sequitur, ut patet in fortiter impellente magnam navem vel maximam lapidem."

35. Summa II, Q.24 (I, 436–37): "Quarto patet hoc: quia nullum eorum, quae educuntur de potentia materiae potest destrui nisi per generationem alicuius alterius; alias eius corruptio esset pura ipsius annihilatio, nisi haberet aliquo modo aliquod ens pro termino; non ens enim non potest esse terminus motus vel mutationis nisi per accidens, cum terminus motus semper si aliquid intrinsecum ipsius motus et plus habens de entitate quam ipse motus; contrarius autem motus vel mutatio non potest esse per se nisi a contrario agente. Igitur si lux et ceterae primae impressiones agentium fierent de potentia materiae, non possent destrui nisi per contrariam generationem et contrarii nec nisi per contrarium agens; quorum contrarium communiter experimur."

36. Summa II, Q.24 (I.437): "Illud autem quod de mixtionibus dicunt non videtur, etiam aliis, aliquo modo verum et multo minus illud quod dicunt quod in aere sit aliquid de veritate omnium formarum corporalium eductum de potentia eius. Quod quia non est omnino directe de materia praesentis quaestionis, ad praesens pertranseo."

37. Summa II, Q.25 (I.440): "ergo actio erit vere effectus alicuius causae agentis et vere informans aliquod subiectum tanquam in ipso recepta."

38. Olivi's theory of impetus has been a subject of discussion from the beginning of modern studies on his philosophy. See Jansen, "Olivi"; Anneliese Maier, Die Impetustheorie; Michael Wolff, Geschichte der Impetustheorie; and Jürgen Sarnowsky, "Concepts." However, we do not find in these studies any attempt to clarify the exact relations between action, species, impression, impulsion, movement, etc. in Olivi's physical system.

39. Summa II, Q.29 (I.503): "Causare enim motum non est semper idem quod movere proprie sumptum; nam levitas ignis non dicitur proprie movere ignem in sursum, quamvis causet eius motum, nec inclinatio data lapidi a proiectore dicitur proicere vel movere lapidem, quamvis causet eius motum; motor enim proprie non dicitur nisi ille qui influit impressionem in mobile per quam ipsum movet."

40. Summa II, Q.23 (I.435): "patiens ab agente non movetur ad formam educendam nisi per inclinationem seu impulsum per quam patiens inclinatur et impellitur ad terminum seu formam per motum introducendam."

41. This is the response given in question II, Q.26 (Quaeritur an primae impressiones omnium agentium fiant ab eis in instanti).

42. Summa II, Q.27 (I.472): "forma non est per simplicem influxum agentis in patiens, sed potius per impulsum datum materiae et non exit in esse tota simul, sed potius successive acquiritur a materia."

43. Summa II, Q.29 (I.502): "in primo virtuali contactu motoris et mobilis seu agentis et patientis patitur mobile a motore; constat autem quod primus contactus eorum fit in instanti; ergo passio facta in mobili a motore in primo contactu eorum fit in primo instanti praedicti contactus; ergo ipse naturaliter praeit motum inchoatum in illo instanti, non autem in ipso possibilem fieri vel esse." It is not entirely clear to us whether "in ipso" refers to the movement or to the instant. However, the meaning seems to be that the contact precedes the movement, and is not potentially given in the movement.

44. For point (3), see Summa II, Q.27, ad 1m (I.502): "forma non est per simplicem influxum agentis in patiens, sed potius per impulsum datum materiae et non exit in esse tota simul, sed potius successive acquiritur a materia."

45. Summa II, Q.26 (I.448): "Circa quaestionem istam est quorudam perspectivorum opinio, ut auctoris Perspectivae, quod agentia corporalia agunt impressiones suas in tempore, licet nobis imperceptibili."

46. Johannes Thijssen, "The nature of change," 281.

47. I. A. Sabra, Theories of Light, 46–48.

48. For an elaborated discussion concerning species as produced in time, see Bacon, Perspectiva, part 1, distinction 9, ch. 3, 135–45.

49. Summa II, Q.27 (I.478): "Formae enim quae de materia educuntur non solum se habent ad eam sicut receptum ad recipiens aut sicut delatum ad deferens, sicut se habet radius solis ad aerem in quo recipitur (non enim radius fit in eo per aliquam applicationem ipsius aeris, sed solum absolute substernitur ipsi radio et receptioni eius); immo ultra hoc [istae formae quae de materia educuntur] se habent ad eam sicut subiectum applicabile et applicatum se habet ad suam actualem applicationem aut ad terminum suae applicationis."

50. Summa II, Q.23 (I.424): "tota impressio quae per profundum seu per continuum sequitur ab aliquo agente, sicut totus radius a luce solari est per se primo ab ipso agente. Unde voluerunt quod totus radius esset primo et per se a luce solari, et non quod pars radii posterior esset a parte priori." See also Q.73 (III.78).

51. Summa II, Q.23 (I.430): "ita quod immediatio excludat causam aliam intermediam, sed tamen non effectum intermedium."

52. Summa II, Q.25 (I.442): "Si agere quo agens agit est aliud necessario a virtute agente et ab eo quod fit in patiente: ergo agere per quod actio agentis facit aliquid in patiente erit aliud ab actione agentis, et sic in infinitum . . . ex quibus sequitur quod agere vel actio sint omnino idem quod primus effectus agentis; sed primus eius effectus est species; ergo etc." The species cannot be considered as something different from the agent's action (A2) for it would lead to a regressus ad infinitum.

53. Summa II, Q.5 (I.96–99). On this text, see David Burr, "Petrus Ioannis Olivi."

54. The theory of 'terminative cause' or 'objective cause' is a specific to Olivi. On Olivi's theory of causa terminativa or causa objectiva, see Juhana Toivanen, Perception, 145–50.

55. Olivi, Epistola, art. 11, 53–54: "Nunquam autem dixi quod agens creatum proprie loquendo producat aliquid de nihilo, quia semper necessario presupponitur materia de qua, aut materia in qua. Prout autem in creatione sumitur ly 'de nihilo,' excludit universaliter necessitatem omnis adiutorii concurrentis, sive illud sit materia, sive dispositio materie, sive virtus instrumentalis agentis et consimilia. Quicumque vero dicit quod omne agens quod producit aliquid cuius essentia non erat prius in materia, vere creat illud, tunc ponit quod voluntas quando producit intra se actum peccati, vere creat actum peccati, nisi forte dicat quod essentia omnium peccatorum erat tota in angelo et Adam et ceteris malis antequam peccarent."

56. We wish to thank Cecilia Trifogli, Nicolas Weill-Parot, Sylvain Piron, Giora Hon, and the anonymous referees for the Journal of the History of Philosophy for their valuable comments on earlier versions of this text.

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