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6. Metaphysics: mind, body and harmony
A basic feature of Leibniz’s metaphysics was his doctrine that everything reflects the entire world in which it exists. This harmony among things derives from God at creation, who adjusts the perceptions of individual substances or monads to one another in creating a world more perfect by virtue of its variety. And so, despite the fact that individual substances cannot communicate directly with one another, and thus have no real metaphysical causal relations with one another, yet there is an extended sense in which what happens in one substance can be considered the cause of what happens in another. Leibniz wrote: ‘The action of one finite substance on another consists only in the increase of the degree of expression together with the diminution of the expression of the other, insofar as God requires them to accommodate themselves to one another’ (Discourse §15; compare Monadology §52). God, in creating a given substance to perform a particular action at a given time, creates all other substances in such a way as to reflect that action at that time. This is what might be called physical causality, as distinct from metaphysical causality which Leibniz denied among finite things.
While every monad or substance is related in some way to every other, there is a special relationship between the mind and the body of a living thing, such as the human being: ‘Although each created monad represents the whole universe, it more distinctly represents the body which is particularly affected by it, and whose entelechy it constitutes. And just as this body expresses the whole universe through the interconnection of all matter in the plenum (that is, space without empty place), the soul also represents the whole universe by representing this body, which belongs to it in a particular way’ (Monadology §62; compare Discourse §33). In this way, the mind is connected with the world by virtue of the special connection it has with the body; on Leibniz’s understanding of causality, mind and body can be the ‘physical’ causes of changes in one another.
So Leibniz solved to his satisfaction one of the central problems in seventeenth-century metaphysics: the interaction between mind and body. Because of the special harmony between mind and body, just when my body is in the state it would be in if it were pricked by a pin, my mind is programmed to have a sensation of pain. And just when my mind is in the state of willing my arm to raise, my body is in the physical state that would result in the raising of my arm, again not because of any direct causal connection (Leibniz to Arnauld, 28 November/8 December 1686 and 30 April 1687). For that reason, Leibniz wrote: ‘According to this system, bodies act as if there were no souls (though this is impossible); and souls act as if there were no bodies; and both act as if each influenced the other’ (Monadology §81). This is what he originally called the hypothesis of concomitance, but called the hypothesis of pre-established harmony when he published it for the first time in the New system (1695b).
The view is summarized in an analogy he often used. The mind and the body can be compared to two clocks that keep perfect agreement. One hypothesis to explain their agreement is that of natural influence, the hypothesis that there is some physical connection between the one clock and the other. This corresponds to Descartes’ view of mind–body interaction, where there is real causal influence. The second hypothesis is that someone watches over the two clocks and, by tinkering with them, always keeps them in agreement. This corresponds to the occasionalism of many of Descartes’ followers, in which mind–body causality is mediated by God who causes sensations in the mind on the occasion of an appropriate bodily state, and actions in the body on the occasion of the appropriate volition in the mind (see Occasionalism). Finally there is the hypothesis that the clocks are so well made that they will always remain in perfect agreement with one another. This corresponds to the hypothesis of pre-established harmony, which Leibniz thought to be the most defensible (Leibniz to Basnage de Beauval 3/13 January 1696).
Leibniz offered a number of arguments directly against occasionalism. He argued, for example, that there must be genuine activity in things themselves because a world of genuinely active things is more perfect than a world of things manipulated by God; indeed, Leibniz claimed, a world of inert things is just the Spinozistic world in which God is the only substance of which other things are modes (‘On nature itself’). He also argued that occasionalism posits perpetual miracles, in so far as God is called in to do that which goes beyond the power of things to do by their own nature (Leibniz to Arnauld, 30 April 1687). As noted below, the conception of the physical world that informs Leibniz’s dynamics is itself a direct challenge to occasionalism. Nevertheless, Leibniz did share at least one important doctrine with occasionalism: that finite substances have no real causal relations with one another. This doctrine may strike a modern reader as eccentric, but it would have been rather less so for a seventeenth-century reader.
Leibniz often presented the hypothesis of pre-established harmony as a solution to the problem of mind–body interaction. But, at the same time, it allowed Leibniz to reconcile the mechanistic conception of the world with a conception grounded in final causes. He wrote: ‘The soul follows its own laws and the body also follows its own; and they agree in virtue of the harmony pre-established between all substances.…Souls act according to the laws of final causes, through appetitions, ends, and means. Bodies act according to the laws of efficient causes or of motions. And these two kingdoms, that of efficient causes and that of final causes, are in harmony with each other’ (Monadology §§78–9). In more concrete terms, behaviour (raising one’s hand, for example) can be explained either in terms of a volition and the harmony God established between mind and body, or purely in terms of the laws of motion, as applied to the physical body. By pre-established harmony, these two explanations will always agree. In this way Leibniz managed to reconcile the dualism of Descartes with the stricter mechanism of Hobbes; everything in the body can be explained in purely mechanistic terms, while, at the same time, Leibniz could also hold that human beings (and other living organisms) have souls which are the causes of much of their behaviour.
In addition to explaining the interaction between mind and body, when first introduced, Leibniz held that pre-established harmony also explains the union of mind and body, that which makes a single substance out of a mind and the collection of individual substances that constitutes its body (Discourse §33). In this way, pre-established harmony provided a central support for Leibniz’s account of corporeal substance. Unfortunately, however, it proved inadequate to the task. In May 1703, René-Joseph de Tournemine pointed out that whatever resemblance one might suppose between two clocks, however justly their relations might be considered perfect, one can never say that the clocks are united just because the movements correspond with perfect symmetry. While it does not challenge pre-established harmony as an account of mind–body interaction, the argument is as simple as it is devastating against the somewhat different claim that pre-established harmony accounts for mind–body unity. In consequence, Leibniz came to question the place of complex corporeal substance in his philosophy, as discussed above (see Malebranche, N. §3; Occasionalism).
Garber, Daniel. Metaphysics: mind, body and harmony. Leibniz, Gottfried Wilhelm (1646–1716), 1998, doi:10.4324/9780415249126-DA052-1. Routledge Encyclopedia of Philosophy, Taylor and Francis, https://www.rep.routledge.com/articles/biographical/leibniz-gottfried-wilhelm-1646-1716/v-1/sections/metaphysics-mind-body-and-harmony.
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