Substance and Matter between Leibniz and Kant

Kant’s discussion of what is involved in there being an actual world in the Inaugural Dissertation contains a refutation of idealism. A merely “perceptual” world is not an actual world, for an actual world must be a set of substances perceived as in interaction with one another and with human knowers. As Kant understood him, Leibniz had maintained that to see an ordinary physical object is to have a confused representation that, if we were to represent it more adequately, would appears to us as what it really is, an aggregate of monads (Cf. G 6: 618ff.)

Leibniz’s metaphysics was developed within, and in part as a reaction to the mechanical philosophy of the mid-to-late 17th century, revived by Bacon, Galileo, Descartes, Gassendi, Boyle, and Locke. While the term “substance,” meaning the indestructible stuff of the universe, was retained by Descartes in his discussions of res extensa, the mechanical philosophers were committed to a corpuscularian theory in which objects were temporary aggregates of solid, indestructible particles with various figures and motions, and all change occurred through their collisions, entanglings, and so on. Leibniz contested the corpuscularian image of the world, insisting that it was insufficiently profound and inherently self-contradictory (G 4: 480), and holding that matter was an appearance founded upon the reality of “metaphysical points” or, as he later termed them, monads: qualitatively unique, unextended, impenetrable, indestructible and partless units that also perceived and strove (G 6: 608.) Kant appreciated the reasons that led Leibniz to posit soul-like entities rather than material atoms as the basic elements of the world. But he was concerned with a very different scientific image. While Newtonian matter-theory was depicted as a rival to Leibnizian immaterialism in the mid-18th century, in for example the Institutions de Physiqueof Mme du Chatelet, Newton was no ordinary corpuscularian or mechanical philosopher, and Kant did not have to contend with that now old-fashioned ontology. His own metaphysics presupposed a Newtonian world held together by forces acting at a distance, one in which the matter of ordinary objects was perhaps only a kind of condensed vapour, as Newton had speculated in Book III of his Principia. Nature had already, so to speak, been dematerialized for Kant by physics, and his Opus Postumum anticipates the romantic nature-philosophy of the 19th century. Matter, he could readily agree with Leibniz, cannot be a thing in itself, stuff possessed of characteristics and qualities independent of human perception; what we call matter is an appearance (4:507.) The inner nature of substances cannot be described by reference to shape, contact or movement, which characterize the objects presented to us. He understood Leibniz’s reasoning in favour of monads as follows: It is impossible to conceive two material atoms as both different from one another and as simple, i.e partless; yet possible to conceive two souls that are both different and partless (20:285.) Therefore, if substances are manifold and partless, they must have representational capacities. The crucial error in this reasoning lay in supposing that our abstract conceptions are a guide to reality behind the spatio-temporal appearances. Yet properly understood, he maintained, Leibniz’s monadology was not an attempt to explain appearances but the expression of a “Platonic” view of the world, considered apart from our sensory experience of it (4:507; 8:248.)

Kant absolutely rejects idealism, but he too believed it possible to deduce some features of matter, as physical science must theorize it, a priori. There are no material atoms; matter is divisible to infinity and its parts are all material (4:503f.) Yet Kant recognized, first in the Physical Monadology, then in the Metaphysical Foundations, particles in the form of centres of attractive and repulsive forces that account for the space-filling property and impenetrability of matter (4: 533ff.) This relatively dogmatic treatment co-exists with his critical claim that matter is the appearance of a perfectly unknown substratum. As he explains it in the Critique of Pure Reason, the rainbow is a mere appearance relative to rain drops which, in a physical sense, are things-in-themselves and not mirages. Yet thinking further, we realize that the raindrops too are mere appearances, and that “even their round form, indeed, even the space through which they fall are nothing in themselves, but only mere modifications or foundations of our sensible intuition; the transcendental object, however, remains unknown to us.” (CPR A45 f./B 63f.) “About these appearances, further, much may be said a priori that concerns their form but nothing whatsoever about the things in themselves that may ground them.” (CPR A49/ B66.) This suggests that the stuff which is divisible to infinity and bears attractive and repulsive forces is an appearance of something unknown and unknowable. “We can understand nothing except what brings with it something in intuition corresponding to our words. When we complain that we do not see into the inner nature of things, this can mean no more than that we cannot grasp, through pure reason, what the things that appear to us might be in themselves…. Observation and division with respect to the appearances take us into the interior of nature, and we cannot say how far this will proceed. But every transcendental question that takes us beyond [perceptible] nature can never be answered….” (KRV (A277f./B333f.)



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