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  • Leibniz and the Two Clocks
  • David Scott

Anyone familiar with Leibniz’s philosophy in general and with his critique of occasionalism in particular is likely familiar with his example of two clocks. Generally speaking, the example illustrates a range of hypotheses that, according to Leibniz, might possibly explain the connections between substances in the world. The most important of these hypotheses are Leibniz’s own doctrine of the preestablished harmony and the occasionalist—for present purposes, Malebranche’s—doctrine of causation. In Leibniz’s mind at least, the two clocks example (so-called because substances are represented by two clocks) illustrates the superiority of the hypothesis of the preestablished harmony over occasionalism. Whether the example in fact succeeds in this regard is the primary question of this paper.

Given the times, Leibniz’s choice of example is understandable. A clock is ideally suited to represent a mechanism, of course; and in view of the general “mechanization of the world view” of that time, the example seems to have been in the air.1 Spring-driven clocks had appeared at the outset of the sixteenth century, and the kind of clock Leibniz seems to have in mind in his example, namely, one driven by a pendulum, was the invention, in about 1656, of Christian Huygens, who was a significant influence on Leibniz. Huygens’s invention in fact provided the impetus for a broadening of the importance and extent of horology.2

Although Leibniz’s choice of example was understandable, it was not a happy one, and the general importunity of his use of this example was [End Page 445] recognized by both his contemporary critics and his subsequent commentators.3 In fact his choice of the example becomes almost ironic when it is recalled that Geulincx, who is most commonly associated with the example, was an occasionalist. The operations of two clocks, between which there is a constant and fixed relation, say, of keeping the same time, cannot normally be said to be “related.” The example is more intuitively taken to indicate the random, accidental, unnecessary, and unconnected nature of the otherwise constant and regular relation between the clocks; and so one would think the example more suited to an occasionalist’s position than to that of Leibniz.

In what follows I aim to judge the effectiveness—in Leibniz’s own terms—of the two clocks example. In gauging the effectiveness of Leibniz’s use of the example, I expect that a few things can be learned about Leibniz’s system in general and about his critique of occasionalism in particular. My procedure will be to examine separately what I take to be four significant occasions in which Leibniz compares things or substances in the world and clocks. The passages in question date from a period spanning ten years, and in each instance the example is put to service in Leibniz’s attempt to better occasionalism.

Beyond this, although the comparison is employed or appraised in slightly different ways each time, the uses to which it is put are basically two. In the first two instances examined below, it is employed primarily to distinguish the preestablished harmony from occasionalism. I will be arguing that, to the extent that it fails to illustrate his point, Leibniz fails adequately to distinguish these two doctrines. This was Arnauld’s criticism.4 In the third and fourth instances, however, the example is employed solely to illustrate certain features of the preestablished harmony. On my analysis, it does not appear to fulfill this role either. [End Page 446]

First Use of the Example

One of the more well known statements of the two clocks example is from an explanation Leibniz gives to Basnage de Beauval in 1696 of his “New System” (1695):

Imagine two clocks or watches which are in perfect agreement. Now this can happen in three ways. The first is that of a natural influence.... The second way of making two clocks, even poor ones, agree is always to assign a skilled craftsman to them who adjusts them and constantly sets them in agreement. The third way is to construct these two timepieces at the beginning with such skill and accuracy that one can...