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In a book on Aristotle's metaphysics I read a passage on the differences between his and Kant's categories. It says that the concept of categories, in both Aristotle's and Kant's case, wasn't conceived by observation of the outside world but is a reflexive concept. Then follows this sentence (my translation):

Unlike Kant, Aristotle obtains his concept not deductively, derived from a principle, but through a type of induction, through abstraction of observable language behaviour.

I understand the induction part of Aristotle's categories, and I know about Kant's categories, but apparently not enough to understand how they can be derived deductively. How can categories, and from what, be derived deductively?

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From first principles, presumably? I would think this might be pointing to Plato's deduction of the form of the good and so on. – Joseph Weissman Dec 1 '12 at 17:35
@JosephWeissman But the text was specifically referring to Kant. I don't think Plato will help here. – iphigenie Dec 1 '12 at 17:41
up vote 2 down vote accepted

To be honest, I suspected that in the normal way of Kant being a Kant, he must've derived his categories transcendentally, which is his modus operandi when it comes to primary concepts. So I searched, and struck gold:

1.4 Logical Forms of Judgment and the Categories

In §§19–20, Kant contends that the vehicle that brings about synthesis is judgment, and that this vehicle employs certain forms of judgment, which are in turn intimately related to the twelve categories. By connecting [synthetic knowledge] to judgment, and the forms of judgment to the categories in this way, Kant aims to show that we must use the categories in the synthesis of experience.

Keep in mind that opinions on what constitutes a synthetic judgment are strongly divided. Kant himself had a very clear idea of what he meant, but may have failed to communicate an exact-enough definition. Julian Baggini points this out in his Toolkit, noting that a way to view the distinction between synthetic and analytic judgments is in whether or not a judgment "adds something to the subject" (§4.3).

What this means for Kant is that in any judgment, there is some experience which is being had. Providing evidence for any proposition requires that an experience of the evidence be possible in the first place. Kant's deduction then unfolds from the argument that categories are a necessary feature of such an experience.

It may appear that Kant has thus plucked his categories out of thin air, but the details of his argument for why experience would be impossible without categories is compelling.

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To be honest, I don't get it. If judgment is needed for synthesis, how can you connect them, and where does it say where the categories come from? I know that we need them for the synthesis, but how does Kant even get to them? Sorry if I'm missing the point of your answer... – iphigenie Dec 5 '12 at 20:43
I'll add a little more. Transcendental arguments are some of the most confusing ones I know of, but the top of that same article includes a good explanation of the form. Wouldn't hurt to pad the answer with a bit more elaboration. – Ryder Dec 5 '12 at 20:57
Thanks, the edit makes it much more clear. I will proceed with the SEP article and tend to agree with your last words. – iphigenie Dec 5 '12 at 21:36

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