Immanuel Kant famously argued that the categories of cause and substance could only apply to the world of empirical experience. The pure concepts of the understanding unite the manifold of intuition in ways that deliver to us objects and events in space and time causally connectable to other objects and events.
To attempt to think metaphysical reality using the categories of cause and substance is, for Kant, to misapply these concepts beyond the bounds of their proper application. When these concepts no longer apply to intuitions -- that is to the spatio-temporal particulars resulting in the application of "pure forms of sensibility" of space and time to the realm of things in themselves -- then their use eventuates in a "transcendental subreption" or "transcendental illusion" of thinking metaphysical reality must be structured in the ways in which our thinking conceives this reality.
By the conclusion of the First Critique, Kant's readers realize that he has indeed provided the necessary philosophical framework to underpin Newtonian mechanics. Instead of holding that substances and causes are in the world apart from human cognition -- and thus being susceptible to the skeptical arguments of David Hume -- Kant places them solidly within the human epistemological domain. While whatever exists apart from us, exists apart from our awareness, perception, conception and language, the empirical order clearly does not. Apart from human beings, there would be no spatio-temporal particulars and no substances which our concepts synthesize from the manifold of sensibility. The phenomenal world, the only world we can know empirically, is nicely ordered causally because we ourselves apply the category of causality and accordingly order the world causally before we empirically investigate it.
Kant believes that the only way to save empiricism -- and thus to be an empirical realist -- is to be a transcendental idealist. If space, time, substantiality and causality were not denizens of our epistemic equipment, the skeptical arguments would finally win the day, and the universality and necessity trumpeted by Newton in his mechanism could never be ultimately justified. In order to have a nature like Newton's, one needed to adopt a transcendental position like Kant's.
So the story at the end of Kant's First Critique is that nature is closed under the operation of physical causality. Physical entities, and the events in which they are ingredient, are causally related among themselves. There are no uncaused physical events, and no physical events causing non-physical events. There is no "free play" in the universe. In order to save Newtonian mechanics, Kant gives us an underlying determinism of a mechanical kind. The world of nature must conform to a deterministic mechanism, because our epistemological equipment process the world in this way. All this is clear.
But Kant did not want to stop writing books after the Critique of Pure Reason. In his Critique of Practical Reason, he argues that the things in themselves, which are only mediatedly accessible through knowing the phenomenal world in the First Critique, are immediately and nominally accessible through an encounter with duty and the moral law in the Second Critique. Now the realm of freedom, responsibility and dignity are opened to human beings; we already are living noumenal reality in our moral experience. While Kant banishes freedom in the First Critique, he gives it back in the Second Critique. The practical postulates of God, immortality and freedom of the Second Critique have no echo in the First Critique. While the latter is the precondition for encounter with the moral law itself, both God and immortality are postulates needed for a complete moral theory, a theory in which the summum bonum is obtainable, i.e., the "highest good" wherein those doing their virtue and thus "worthy of happiness," can be, in fact, recipients of that happiness.
Prima facie, the results of the first two Critiques seem to be in tension with each other. How can a human being with a body possibly have free moral experience when the bodies in and through which that moral experience is had are denizens of the phenomenal realm and its mechanistic determinism? Nobody can do the right thing, it seems, without an act that is somehow physically expressed. One cannot help a little old lady across the street without a body. One cannot bring about the good if one cannot bring about anything at all. If nature is the realm of the bodily, and human beings have bodies and presumably act in and through them, then how can one ever do that which is better than some other act. If the phenomenal realm is the realm of "one cannot do other than one did do," and empirical reality is coextensive with the phenomenal, and if human freedom is "one can do other than what one did," then how can freedom be exercised for coporeal human beings? If one do other than what one does do, then deterministic mechanism is false, and if physical entities cannot do other than what they do, then human freedom is impossible.
Fortunately, Kant wrote another book, one that is not read as often by philosophers these days, but nonetheless must appear within the top 100 of philosophical classics. This book is entitled Der Kritik der Urteilskraft, translated as The Critique of Judgment, though a better translation would have been The Critique of the Power of Judgment. In the Introduction to this book, Kant claims that he wishes to reconcile the two earlier Critiques, and introduces the notion of a reflective judgment. Unlike a determining judgment which operates determinately to think a given particular under a given universal, the reflective judgment is one wherein their is freedom to think a universal on the basis of the particular. It provides, as it were, some "free play" in understanding the particular. After introducing this, Kant launches into a wide-ranging and very famous discussion of the notion of beauty and related concepts, followed by a discussion of teleology and purpose in their relationship to the aesthetic. Many readers become frustrated in the The Critique of Judgment because it does not seem that Kant ever gets around to providing a sustained argument for what is promised: a reconciling of the results of the first two Critiques.
It is possible, however, to provide an overview of his intended "solution." The relevant sections of the Critique are these: #8 and #9 in the Introduction, and #70 - #85 in the Dialectic of Teleological Judgment and the Methodology of Teleological Judgment.
In #70 Kant distinguishes reflective and constitutive antinomies.
- Thesis of reflective judgment: "All production of material things and their forms must be judged to be possible in terms of merely mechanical laws."
- Antithesis of reflective judgement: "Some products of material nature cannot be judged to be possible in terms of merely mechanical laws."
- Thesis of constitutive judgment: "All production of material things is possible in terms of merely mechanical laws."
- Antithesis of constitutive judgment: "Some production of material things in not possible in terms of merely mechanical laws." (Pluher, 267, KU 367).
Kant points out the the thesis and antithesis of a constitutive judgment are antinomies or contradictories, i.e., the truth of one entails the falsity of the other. In other words, they cannot both be true at the same time. But Kant does not believe that the first two statements are contradictory:
But if we consider instead the two maxims of a power of judgment that reflects [i.e., the first thesis and antithesis above], the first of these two maxims does in fact not contradict [the second] at all. For if I say that I must judge all events in material nature, and hence also all the forms that are its products, in terms of merely mechanical laws as to [how] they are possible, then I am not saying that there are possible in terms of mechanical laws alone (i.e., even if no other kind of causality comes in). Rather, I am only pointing out that I ought always to reflect on these events and forms in terms of the principle of the mere mechanism of nature, and hence ought to investigate this principle as far as I can, because unless we presuppose it in our investigation [of nature] we can have no cognition of nature at all in the proper sense of the term" (267-68, 387-88).
What is going on here?
Clearly, Kant is understanding a reflective judgment to be quite different than a determining or constituting judgment. In the First Critique, Kant had laid out the transcendental conditions for the possibility of experience as such -- an experiencing of empirical nature in Newtonian ways -- as the determining judgments under which intuitions fall. The result is a mechanistic determinism. But does Kant's move to a reflective judgment allow him to escape the charge that just as there is a contradiction between the thesis and antithesis of a constitutive (determining) judgment, so there is a contradiction between the thesis and antithesis of a reflective judgment? Is this not a case of what is good for the goose is good for the gander?
The key to holding that there is no antinomy in the reflective judgment rests upon the ability of the thinker to recognize that the reflective principles in question are heuristic, that far from "carving the beast of reality at its joints" (Plato), they simply are principle by which we might think nature. We attempt to see nature as entirely deterministic, but it is possible that that we adopt a different principle for regions of our empirical investigations. (Think of how difficult it would be actually to give a mechanistic/deterministic account of beavers building a dam. One could not use the category of final causality or employ any implicit purposeful functionalistic explanations, e.g, the beavers are acting this way "in order to" bring about some state of affairs.) It might allow us to understand more about nature to employ the reflective judgment that "some products of material nature cannot be judged to be possible in terms of merely mechanical laws." Something more is needed.
Kant reconciles the two reflective judgments because there is supersensible ground allowing both judgments to be used heuristically, if not descriptively. Kant writes:
If we are to have a principle that makes it possible to reconcile the mechanical and the teleological principles by which we judge nature, then we must posit this further principle in something that lies beyond both (and hence also beyond any possible empirical presentation of nature), but that nonetheless contains the basis of nature, namely, we must posit it in the supersensible, to which we must refer both kinds of explanation" (297, 412).
But what is accomplished here? It seems that the thesis and antithesis of the antinomy of reflective judgment still form a contradiction. Yet Kant is suggesting that this clear and present contradiction is "taken up" by the reality of the supersensible of which the thesis and the antithesis are partial grasps. So the supersensible substrate supports a coincedentia oppositorum in a way not unlike how God could only be thought in the mystical traditions through dialectical formulations. 'All P is J' and 'Some P is not J' are contradictories and cannot be other. However, these contradictions are somehow sustained in the ground of the supersensible. We are permitted to use either because the nature of the supersensible cannot be articulated by either. When one says them both, one learns something about that which cannot be known.
The fundamental problem of philosophy since the time of Decartes has been this: "How is human freedom possible in a determinstic physicalist universe?" Kant is taking on this big question and saying that the problem is one of thinking how it is possible, not it being possible. It is possible after all, because it is actual. The supersensible substrate is worked up mediately in the First Critique, more immediately in the Second, and these varying accounts put together in the Third. We can't do metaphysics, so cannot carve this "beast of reality." We will always end in antinomies when we do. But nonetheless the supersensible grounds the possibility of corporeal entities acting freely. Purposefulness in nature attests to an opening by which freedom can be instantiated in a physical system.
Kant says that the antinomies of reflective judgment are not antonomies because the truth of one does not entail the falsity of the other. He might have better started to index judgments to standpoints. Clearly, the antinomies are contradictories for us and how we must think the universe. They are contradictory coram hominibus. But they are not contradictory from the standpoint of the supersensible. That is, they are not contradictory coram deo -- if we might apply that term here. Kant knew that ultimately the tools of human understanding and thinking simply were inadequate to think reality as such.
