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A couple of days ago, I got embroiled in yet another discussion with a person of considerable (and well deserved) academic reputation in philosophy, who steadfastly maintained that Kant was “just another rationalist in the footsteps of Descartes.” That, of course, is wrong on so many levels that it requires a somewhat lengthy post.

The rationalists of the 17th Century, in particular Descartes, were children of the Age of Faith. Descartes’ distrust of the senses, a suspicion he shares with the Platonic tradition, is entirely compatible with the rejection of the flesh by the church in the Middle Ages. Descartes didn’t set out to replace faith with reason, but rather to provide an alternative path to knowledge of god, soul, and the world (metaphysica specialis). Descartes, along with many of his contemporaries, realized that the foundations of religious inquiry into these matters, relying on sources such as revelation and dogma, were shaky. And so he set out to reason his way from an unshakeable foundation, a fundamentum incocussum, to the entire body of knowledge as it existed at the time. Descartes’ starting point, famously, was the reflexive sum res cogitans or cogito ergo sum, whereby the act of reasoning itself proved to be the only thing that could not be doubted. That starting point didn’t get him very far, so he had to introduce a very limited notion of god as a guarantor of an intelligible external universe, and from there the rational reconstruction of knowledge could and did proceed.

That was the kind of speculative metaphysics, rationalism run wild, against which Kant rebelled. But Kant, unlike Hume, didn’t reject rationalism per se, because above all, Kant was a devoted Newtonian. Kant was firmly on the side of the new natural philosophy, the engine of enlightenment, which later would mature into the natural sciences. But here was the problem: Newtonian physics was a highly theoretical, mathematically sophisticated undertaking and by no means particularly empirical. Empirical observations, in fact, were more or less relegated to confirming models and hypotheses. What was so striking about Newton’s physics was that for some strange and prior to Kant inexplicable reason, nature seemed to obey mathematics. Galileo was an empiricist, but because of that his inquiries, while groundbreaking, could only get so far. Newton, on the other hand, liberated natural philosophy from its rigid empirical shackles and turned it into a primarily (but importantly not entirely) theoretical inquiry. Newton supplied the mathematical apparatus on which early modern science was built, and in which the world was described as matter in motion within a causally determined universe. Why was that a problem? Because Kant could not abandon rationalism wholesale. There was “good” rationalism, embodied by Newton’s physics, Euclidian geometry, and Leibniz’ version of the calculus (the only contribution of Leibniz that Kant would tolerate), and there was “bad” rationalism, such as Descartes’ attempt at continuing metaphysica specialis by different means. Hume’s subjectivism (natural laws are just habitual expectations of regularity), would wipe out both kinds of rationalism, and that was a consequence that Kant could not accept. For him, it was “the destruction of all knowledge.”

Hence the Critique of Pure Reason. Reason, and that means rationalism, is an addict by nature. Specifically, reason is addicted to speculative expansion (”spekulative Erweiterrungssucht”). The German text is quite explicit about the addictive qualities of speculation, a connotation that seems to have been lost in the English translations. The Critique is a detoxification program. Reason, and thus rationalism, is the path to knowledge, provided that reason doesn’t get high on itself. But once reasoning gets underway, where do we stop? Kant’s answer: At the bounds of possible sense experience. Note the remarkable similarities to modern rational empiricism. We create models of the world using ever more sophisticated mathematical tools, and we use experience, massively aided and amplified by technological tools, primarily in a confirmatory (or falsificatory) manner. In other words, we don’t just induce theories from our experiences, because beyond the relatively obvious that just doesn’t get us very far. Most of the work in modern science is theoretical. Kant understood that part much better than Newton himself, who famously - but mistakenly - declared: “Hypotheses non fingo.” In any event, theoretical modeling plus empirical confirmation at the fringes is precisely what Kant envisions with his concept of “sober” rationalism within the bounds of possible experience.

His solution to the problem, of course, is as brilliant as it is notorious. The world conforms to Newton’s laws of physics, because we bring those laws to the party. We cannot perceive the world in any other way. So no matter what’s really out there (the noumenal world), once consciously perceived, the phenomenal world will always obey the laws of its subconscious construction. That explains why the world obeys Euclid and Newton, but that explanation comes at a price, which is twofold. First, Kantian constructivism makes truly objective knowledge impossible. For some, that’s a significant loss. Second, and this was the point that troubled Kant more than anything, Newton’s causal determinism left no room for free will in the phenomenal world. Kant would try to solve this problem in the Critique of Practical Reason, but that attempt never fully got off the ground.

What should we make of this? Kant clearly overestimated the timeless nature of Newtonian physics (and of Euclidian geometry for that matter). Einstein undermined the matter-in-motion paradigm, Heisenberg successfully questioned the assumption of causal determinism, and non-Euclidian geometry managed to model certain strange parts of the world out there with great success. Our cognitive firmware received a massive update in the early 20th Century. Today’s categories and forms of experience are different from those in Kant’s days. And so we can reconcile Hume and Kant to some extent, which might not come as a surprise, given that it was Hume who woke Kant from his “dogmatic slumber” in the first place. Hume was right about the tentative, psychological nature of the natural laws. But it was Kant who understood that in uncovering those laws, we recognized ourselves, that is, the work of our own engines of world construction.

In other words: “No, Kant was not just another rationalist in the footsteps of Descartes.”

[tags]philosophy, Kant, Descartes, Hume, rationalism, idealism[/tags]

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