This morning I'm thinking about Kant. Usually these days for me, Kant is a big source of a sort of rampant Cartesianism that I see in the classroom and in the popular culture. This is a teacher's perspective. His idea that the mind projects a conceptual structure onto the world (Kant thought that space and time, cause and effect, were more creations of the mind than perceptions of real being) is variously presented as obviously the thesis of Plato and as obviously the thesis of Nietzsche, and I've even encountered people who insisted that Plato and Nietzsche were complete opposites and that they were both Kant. All the facile rhetoric of "I believe what I believe, you believe what you believe" that we swim in seems to smell of Kant (is it the same river that smells of Kant from day to day?). It also appears to me that Kant, in his insistence that a transcendent rationality was what set humans (to be fair, he's careful to always say "any rational beings") apart from the rest of creation, and that ethical thinking is just equivalent to rational thinking applied, is indeed very like Plato. So I often think of Kant (Hume guy that I am) as the representative of the old regime, a synthesis of Plato and Descartes to be undone by the "bottom-up" post-Enlightenment scientists.
So I got to thinking when I saw in a post on Tractatus Blogico-Philosophicus that cited Schopenhauer as writing that Kant "had circumnavigated the world and shown that because it is round, one can not get out of it by horizontal movement." Kant saw himself as saying something new, notoriously comparing his own insight to that of Copernicus. I think that roughly the idea is that the classical tradition sought for an external cause of the intelligibility of the world (The Good, God), whereas Kant had demonstrated that the intelligibility of the world could only be understood as a property of the mind. So the irrationality of faith that is emphasized in Kierkegaard and Nietzsche is present in Kant's formulation that God, like freedom, must be a part of the ineffable noumenal world. But on Kant's view Mind is just as metaphysically separate from matter as Form ever was for Plato. He just took over from Descartes the task of additionally sticking us in our heads. Still it's technically speaking very modern for Kant to argue that a lot of traditional metaphysics just couldn't be done, as things couldn't be known otherwise than as how our minds organize the representations of things. Totally Cartesian.