In his essay On Nature Itself, or on the Inherent Force and Actions of Created Things, Leibniz attacks the occasionalist doctrine of causation as presented by his contemporary John Sturm, in his De idolo naturae. The motivation for Leibniz’s attack rests in his conception of simple substances as possessed of "a sufficiency…which makes them the source of their internal activities, and renders them, so to speak, incorporeal Automatons" (Monad. 18). Leibniz’s ideas about substance form the basis for his more encompassing notion of a universal relationship of interdependence amongst monads (i.e., his "pre-established harmony"). Thus an examination of the broader implications of our analysis of Leibniz’s attack on occasionalism will also be in order.

Sturm’s metaphysical opinions may be tentatively categorized as Cartesian in nature, in that they seem to arise from a deep conceptual split between the human and the natural: on the one side there is mind and free will, and on the other, there is automata. On this interpretation, Leibniz’s strategy for attack may be basically reduced to an insistence that a physicalist description of nature fails to exhaust the information which particular natural substances must contain on order for a cohesive universe to subsist. The information in question is that represented by perceptual experience itself. Indeed, for Leibniz the fundamental principle of change in the universe "…is nothing else than what is called Perception" (Monad. 14). Leibniz’s attack on occasionalism thus constitutes an attack on physicalism as well. He makes this side of his attack explicit in his Monadology, when he claims that "…Perception, and that which depends upon it, are inexplicable by mechanical causes…" (Monad. 17).

Leibniz notes that Robert Boyle, of whom Sturm’s writings constitute a defense, believes that "…we must hold nature to be [nothing more than] the mechanism of bodies itself" (ONI. 810). Leibniz objects that although such a characterization is superficially adequate, it does nothing to explain the "how" of such a mechanism: "we must distinguish principles from derivative matters…it is not enough in explaining a clock to say that it is moved by a mechanical principle, without further distinguishing whether it is driven by a weight or a spring" (ONI. 810-11). In other words, we must ask how the mechanism of nature functions, rather than simply note that it does.

Sturm’s response is that the activity that we see in nature is "…now taking place…by virtue of an eternal law once established by God, [i.e.,] a volition [or] command…" (ONI. 812). There simply is no "how," other than that God has commanded it. The how is simply one of the unfathomable mysteries of God, and as such, must remain wholly beyond our ken.

In fact, Sturm’s views retain this skeptical (and rather Humean) flavour as they apply to the phenomenon of motion: "motion, he says, is merely the successive existence of the thing moved in different places" (ONI. 820). Leibniz scores an easy point here in noting that this statement "expresses the result of motion rather than what we call its formal reason" (ONI. 820). In my opinion Leibniz is here being too light on Sturm; Sturm’s statement barely makes sense, and certainly exemplifies a kind of Orwellian doublethink at its best (or worst). It can be restated as the following: "motion is the way a thing appears as it is being moved." In effect Sturm seems to be trying to deny the existence of motion and affirm rather that it only appears as if there were motion — but he assumes the existence of motion ("a thing moved in different places") in order to do so! Leibniz points out this contradiction in Sturm’s thinking when he notes that "…[Sturm] denies that created things by themselves properly act, yet he nonetheless admits that they do act, since he is unwilling to have ascribed to him the comparison of created things with an ax moved by a woodcutter" (ONI. 816).

Leibniz argues that within Sturm’s explanation the command of God produces "…only an extrinsic denomination" (ONI. 812) on things. Leibniz argues that such a denomination is insufficient to account for action. Leibniz wants not only to account for the appearance of movement, but also for movement itself; thus he sides with Gunther Schelhammer in arguing for "…an internal law from which [the] actions and passions [of things] follow" (ONI. 812).

Leibniz proceeds by offering a concrete argument for his view. He claims that since the command of God was given in the past, it "no longer exists at present, [and] can accomplish nothing unless it has left some subsistent effect…which has lasted and operated until now" (ONI. 813). It should be noted that Leibniz is not disputing that ultimately it is God who is responsible for the activity in nature, but rather he is simply arguing that there must be some power or "…connection, either immediate or mediated by something..." (ONI. 813) which links the cause (i.e. God’s will) with the effect (i.e. the operation of nature). To claim that something causes something else without admitting the necessity for some kind of link through which this cause can operate amounts to the claim that "…anything can be said to follow from anything else with equal right" (ONI. 813).

Also considered and rejected by Leibniz is the possibility that God continuously and for all time personally provides the force necessary for movement to take place. God would thereby be recreating the universe at every moment. Leibniz rejects this idea (i.e., occasionalism proper) outright as reprehensible and possibly heretical, saying that it is everyone’s "own affair to decide how worthy he considers this of God" (ONI. 815).

One of Leibniz’s more central arguments with regard to a force inherent in nature concerns his ideas about the nature of substance. He makes the claim in On Nature Itself that "the substance of things itself consists in the force of acting and being acted upon" (ONI. 815). He offers a small reductio-style argument in support of this claim, namely that without such a force the whole history and future of the universe would reduce to nothing more than a series of "…evanescent and flowing modifications or phantasms…of the one permanent divine substance. And, what reduces to the same thing, God would be the nature and substance of all things — a doctrine of most evil repute" (ONI. 815).

In order to avoid pantheism and stay within the confines of accepted Christian doctrine, Leibniz contends that we must admit that a motive principle exists outside of God. Thus he refines the principle that "…the same quantity of motion is preserved" to the following: "…that the same quantity of active power is necessarily conserved" (ONI. 811). He likens this active power to an "impression" left by God’s command, even going so far as to say that "the law set up by God does in fact leave some vestige of him expressed in things….a form or force such as we usually designate by the name of nature" (ONI. 813). Leibniz notes that Sturm himself professes a similar view, such as when he says that "…a certain particle of divine power…must be understood in a sense as belonging to and attributed to things" (ONI. 824). However, Sturm never expounds upon the consequences of this view, and seems to contradict it in various other passages of his work.

Based on these remarks it is easy to see how one might charge Leibniz as himself holding a subtle kind of pantheism. If nature is simply a "vestige" of God, then how different is that from Sturm’s view, or even that of Spinoza? Clearly, Leibniz must answer this charge if he is to maintain his view that there are genuine causal agents apart from God.

Some important passages relating to this question appear in the Monadology. Leibniz there claims that "while souls in general are living mirrors or images of the universe of created things, minds are also images of the Deity himself or of the author of nature….each mind being like a small divinity in its sphere" (Monad. 83). He goes on to claim that the relationship between God and created minds is less like the relationship between an inventor and his machine as it is between a prince and his subjects, or even a father and his children (Monad. 84). This analogy is quite helpful in deciphering what Leibniz means by calling nature a "vestige" of God. No one would dispute that a parent is ontologically separate from his children, but it could be said that children are the "vestiges" of the parent. Although the parent causes the children to exist, the children, once existent, are causal agents in themselves.

If such vestigial features are removed from one’s ontological picture of the world, it would follow that even the workings of one’s own mind would exist merely as mechanisms powered by the will of God. As Leibniz notes, such a view "…seems foreign to reason as no other view can be. For who will doubt that the mind thinks and wills, that many volitions are produced in us and by us, and that there is something spontaneous about us? To doubt this would be to deny human freedom and to thrust the cause of evil back into God but also to contradict the testimony of our internal experience and consciousness…" (ONI. 817). Without an active power in nature, our own minds become mechanisms somewhat more complex, but essentially no different, than the machines which we ourselves manufacture.

At this point one might object that when we speak of "nature" we commonly think of it as distinct from humanity. Although it may be absurd to speak of humans as mere mechanisms without any will or personal power of their own, perhaps the same absurdity fails to apply to non-human nature. Indeed, it seems odd to speak of rocks, for example, as being "children" of God, the vital difference being that rocks (one assumes) do not have minds.

Leibniz addresses this point in various passages. He claims in the Monadology that "the body belonging to a Monad, which is its entelechy or soul, constitutes together with the entelechy what may be called a living being, and with a soul what is called an animal" (Monad. 63). He claims further that "the machines of nature…that is to say, living bodies, are still machines in their smallest parts ad infiinitum"(Monad. 64) and that "there is a world of created things, of living beings, of animals, of entelechies, of souls, in the minutest particle of matter" (Monad. 66).

That the mechanism of nature is a living mechanism is important in that it means that all simple substances perceive. In fact, Leibniz claims that "…there is nothing besides perceptions and their changes to be found in the simple substance" (Monad. 17). Since, as was already noted, it is impossible to find anything that we could identify as perception simply by studying the inner workings of a machine, it follows that there is more to nature than mere mechanism.

We must be careful here, however, since Leibniz does not mean to imply that all substances "feel." As he puts it, "…feeling is something more than a mere perception" (Monad. 19). By claiming that all substances perceive, Leibniz means simply that all substances have "…relations which express all the others…" (Monad. 56). Without perception, every substance would be isolated from all the rest, existing only as a phantasm without the ability to affect or perceive anything else. There would be no "one world," but rather only a series of worlds devoid of content other than the arbitrary imagery that God would have provided them with.

By claiming that nature is merely a mechanism without any inner force of its own, Sturm seems to be looking solely at the superficial appearances of things. Ironically, he ignores the most superficial appearance of all, namely the very fact that he is perceiving and thinking. By treating the entire world as a machine, Sturm must necessarily think of each part of that machine as no more than a component of something larger, incomplete in itself. In order to deal with the fact of perceptions and of personal will, Sturm must either deny their existence, thereby putting himself in an absurdly dubious metaphysical position, or consider them simply as working components within the mechanism. If he did the latter he would be in line with Leibniz’s position, although he would be stretching the accepted definition of the term "mechanism."

Leibniz’s view makes an independent machine out of every part of the universe, complete with its own proper power source and product. We can think, within Leibniz’s system, of perceptions as being the "products" of the mechanisms of nature, (in fact Leibniz himself uses this metaphor in section 17 of his Monadology), although in reality the perceptions and mechanisms exist for Leibniz in different spheres, such that both bodies and souls act independently of one and other, "…and yet both…act as if the one were influencing the other" (Monad. 81). The reason that corporeal and incorporeal substance seem to affect one and other is that "they are fitted to each other in virtue of the pre-established harmony between all substances, since they are all representations of one and the same universe" (Monad. 78).

Here we get to the last and most vexing problem with regard to Leibniz’s ideas about substance and causation. Leibniz claims in On Nature Itself that "…the intercourse of substances…arises not from an influence but from a consensus originating in their preformation by God, so that each one is adjusted to the outside while it follows the internal force and laws of its own nature" (ONI. 817). This statement seems paradoxical for various reasons, and may in fact fall prey to Leibniz’s own objections to occasionalism.

Firstly, if God has created all substances such that they will be in harmony with each other for all time, it seems strange to say that their actions are the results of their own power. This is really a variation of an old objection against anyone who believes both in an omnipotent deity as well as in free will. There are various ways that the theist can attempt to overcome this problem; in Leibniz’s case, a distinction is made (for example in section 13 of his Discourse on Metaphysics) between the certain and the necessary. Although everything that will ever happen with regard to every particular substance is certain, it is not necessary, and thus, Leibniz thinks, substances are free to act as they see fit.

This objection works also in an opposite fashion when applied against Leibniz, due to his beliefs concerning the divisibility of substance. He notes that each machine in nature freely follows its own internal laws, but that when it comes to their intercourse with machines external to them the momentum of the pre-established harmony comes into play. The problem is that, as has already been mentioned, Leibniz asserts that the machines of nature are infinitely divisible, made up of smaller and smaller machines ad infinitum (see section 64 of his Monadology). If we pick a machine at any level within this infinity, we must be prepared to accept that it operates with regard to its own internal (appetitive) power. Thus a human being is made up of an infinite number of smaller powers, each with its own perceptions and appetites (and motions; see section 65 of the Monadology). It is hard to see how a human being can operate of its own free will as well as be the result of an infinite number of other wills. Thus not only must Leibniz defend free will from above (i.e. from God), he must also defend it from below (i.e. from the smaller particles of which a human is composed).

Leibniz can respond to this problem by noting that although our bodies are made up of an infinite number of smaller bodies (and therefore smaller creatures), the totality that is us is indivisible. There are monads at every level of the mechanism of nature, and each is simple, devoid of constituent parts. These parts work together in virtue of God’s establishment of a perfect harmony amongst them.

The question as to whether Leibniz’s system actually incorporates occasionalist elements hinges on what Leibniz really means by saying that the power in nature is a "vestige" of God. He also terms this vestige "…an expression, an imitation, a proximate effect of the divine power…" (ONI. 824). If the power in nature is itself a "proximate effect" of God, and it serves to link the cause that is God’s original command to the effect that is the motions of things in nature, then how far is this from saying that all of nature’s motions are direct effects of God? Perhaps quite close…or perhaps not close at all. For even if all of nature is simply following God’s command, there must be something there that is being commanded — as well as actively following that command. To return to Leibniz’s analogy of the prince and his subjects, only the most egotistical of princes would claim to have defeated a rival nation single-handedly, that is, by using his army. The Leibnizian world seems more like a perpetual motion machine than a machine with divine batteries: although its motions will always follow a design, and although it requires a divine push to get started, it will work on its own until God decides otherwise.

Works Cited

Leibniz, Gottfried Wilhelm. Discourse on Metaphysics / Correspondence with Arnauld / Monadology. Trans. George Montgomery. La Salle, Illinois: Open Court Publishing Company, 1995.

Leibniz, Gottfried Wilhelm. "On Nature Itself, or On the Inherent Force and Actions of Created Things." Philosophical Papers and Letters. Ed. And Trans. Leroy E. Loemker. 2 vols. Chicago