Kant resolves the contradiction in the Third Antinomy (#23) as he resolves the others, by throwing each side into a different mental box: the thesis, he says, is a principle of the Understanding, and the antithesis is a principle of Reason. But a deeper problem now arises.
Here again we see how tightly history of philosophy’s web is woven, for this new problem had also made trouble for Aristotle. His divine Prime Mover, being without matter, cannot change. But any action of a cause, Aristotle says, changes the cause: saws, for example, become dull. So how can something unchanging be a cause?
This was also a problem for Plato, but one he perhaps didn’t see clearly, for he never really explains how a form causes a thing to participate in it at a particular time: “participation,” Aristotle remarks, is a word and not a theory.
So Kant’s problem goes back to Plato; but his solution remains with Aristotle, who presents it in Metaph. Λ. There he asserts that there is one kind of cause which does act without changing, and that is the final cause. Love is an example: the person you love changes you, but your love does not necessarily change them; unreciprocated love is quite common. So the order of nature must be caused by the love of the cosmos for the Prime Mover, which acts ὥς ἐροῦμενον—as something loved. And love for Aristotle is a form of final causality: to love someone is to become more you in their proximity.
And Kant? On the one hand, he is going to say that we are not talking about objects, as Aristotle and Plato were; and we are also not talking about our experiences, as Hume thought. Nor, to be sure, are we talking about love. We are talking about fundamental, unalterable activities of the mind which proceed according to rules. The Understanding follows the thesis of the Third Antinomy, taking as its rule of operation that everything has a cause outside itself; the antithesis follows Reason, which takes as its rule the possibility of a free action, i.e. one without such a cause. So the Kantian question is: how can we view Reason as a cause without violating the rules of either faculty?
The First Critique, that of pure Reason, suggests that simply relocating the issue to the faculties solves the problem: our minds are set up to work with two contradictory rules, end of story. The Second Critique, that of practical Reason, maintains that Reason acts as a cause via a feeling, that of respect (Achtung) for the moral law—the only a priori feeling that we have. This solution is more than a bit ad hoc, and because it is restricted to a feeling it does not explain how it is even possible that an individual moral action can make the world a better place. So in the Third Critique, that of Judgment, Kant goes back to Aristotle, and invokes his solution to the problem.
It is not that an old bachelor like Kant makes ἐρῶς into a moral force. But Aristotle, recall, believes that ἐρῶς is a kind of final cause: I love someone because I become more myself in their vicinity. And this suggests a more general answer to the question of how something immutable can be a cause: if something else tends to imitate it. Kant argues that the faculty of Judgment takes it as its rule that the sensory world, structured by the Understanding according to external causes, seeks to become a world of Reason, structured by free actions. Or at least: Judgment has to view it that way.
The stakes here are sky high for Kant. If he is right, but only then, he has answered how the two contradictory rules of the Understanding and Reason can be united into a coherent human mind; and, moreover, he has explained what Plato and Aristotle—and everybody else running around in the ancient Metaphysical Barn—could not: how the immutable realm (Reason for Kant, forms for Plato, essences for Aristotle) relates to the changeable world we live in. The price of this, for Kant, is that we are talking not about objective reality, but about the way the rules of our mind make us see such reality.
Kant is willing to pay this price; but he cannot, for he does not do even the job his critically restricted philosophy requires. His “argument” that Judgment requires us to see nature as having Reason for its final cause (at Critique of Judgment §§ 82-85) is not even an argument, but a series of observations, digressions, stipulations, and the like.
So here is where things stand after the Critique of Judgment: Hume has shown that we can have no knowledge of immutable things outside our mind; Kant agrees with that, but then tries to establish such knowledge within the mind, in the form of the (knowable) rules of the faculties. He then cannot explain how the immutable truths of Reason can serves as causes in the ever-changing world we actually live in. His failure means that immutable truths cannot be known either inside or outside of the mind. Philosophy must dismiss them altogether
Hume’s success led him to billiards, and then to history. What happens after Kant’s failure?
The Critique of Judgment came out in 1790. Philosophy held its breath for 17 years.