Question I'm going to be a senior in high school and I've found philosophy podcasts to be a great way to sample the thoughts of famous philosophers without having to drudge through esoteric forests of essays. Between listening to Philosophy Bites and Nigel Wharburton's reading of his book Philosophy: The Classics, I've become familiar with a bit of Hume and Kant. It is probable that I have misunderstood much of the material of the podcasts, so the material of this question does not reflect in any way the reliability of the sources. As I understand, Hume proposed the a priori and the a posteriori, the latter constructed by experience. Kant then respected the two categories but divided them into analytic a priori, synthetic a priori (new after Hume), and synthetic a posteriori. What interests me is the problem of "the missing shade of blue." Because all ideas originate from experience, even simple ones like fundamental colors (or shades of them), then are not all colors a posteriori? For they cannot be a priori in the instance of a blind man. To reconcile the problem of whether one can imagine a missing shade of a color wheel, and furthermore define the means by which he may do this, might Kant have had an opportunity to further classify and suggest that experienced colors belong to the category of an 'analytic a posteriori' and imagined colors belong to the synthetic a posteriori (because they are 'produced' from the relations between two experienced impressions)?

Accepted:
September 2, 2010

Comments

Although Hume does not himself use the terms 'a priori' and 'a posteriori', those categories do, roughly, correspond to the distinction that Hume draws between relations of ideas and matter of fact in the Enquiry Concerning Human Understanding. (The Enquiry Concerning Human Understanding is also referred to as the 'first Enquiry', as I will do in what follows, to distinguish it from the Enquiry Concerning the Principles of Morals, the 'second Enquiry'.) Now, by the by, but interestingly enough, Hume doesn't draw the distinction between relations of ideas and matters of fact, at least explicitly, in the earlier Treatise of Human Nature, much of whose first Book was recast in the first Enquiry, although he does draw a related distinction in Book 1, Part 3, Chapter 1 of the Treatise, between relations that depend on 'intuition' and 'demonstration', and have only to do with ideas, in contrast to other relations, which do not so depend on ideas, and thus do not admit of the sort of certainty characteristic of intuition and demonstration.

Near the beginning of Part 1 of Section IV of the first Enquiry, Hume explains that relations of ideas "are discoverable by the mere operation of thought, without dependence on what is any where existent in the universe," whereas, by contrast, matters of fact "are not ascertained in the same manner...the contrary of every matter of fact is still possible, because it can never imply a contradiction, and is conceived by the mind with the same facility and distinctness, as if every so conformable to reality." Insofar as relations of ideas do not depend "on what is any where existent in the universe," they are akin to Kant's analytic truths, which depend, roughly, only on the meaning of their terms; matters of fact, which do depend on what is existent in the universe, depend on experience, and thus are akin to Kant's synthetic truths. As you quite rightly point out, there is no room in Hume's division between relations of ideas and matters of fact--which is sometimes called 'Hume's fork'--for the category of the synthetic a priori, which seems to straddle the realms of relations of ideas and matters of fact and thus to explode that supposedly exhaustive division.

Now you want to bring these distinctions to bear on Hume's famous thought experiment of the 'missing shade of blue', which he himself took to constitute a prima facie counterexample to his claim that all ideas are derived from impressions, that is, that all thoughts may be traced back to experience. (It's worth noting that in both the first Enquiry and in the Treatise, Hume actually considers the missing shade of blue before he introduces the distinction between judgments based on experience and those not based on experience and hence admitting of certainty. He therefore must not have thought that his 'fork' was related to the missing shade of blue.) The missing shade of blue might seem to constitute a counterexample to this view, because in this case, the thought of a color is arrived at without one having had experience of that previous color. Now Hume himself, after propounding the example, says that although "this may serve as a proof, that not every idea is derived from correspondent impressions...this instance is so singular, that it is scarcely worth our observing, and does not merit, that for it alone we should alter our general maxim." Although Hume may have thought the missing shade of blue "scarcely worth our observing," his readers have given it considerable attention, and you propose that one might understand the example, in Kantian terms, as marking a distinction between imagined and experienced colors, with the latter belonging to the category of the 'analytic a posteriori' and the former belonging to the 'synthetic a posteriori'.

It's not clear to me that this suggestion can work. After all, analytic judgments, for Kant, are not supposed to depend on experience, so it does not seem to me that judgments about colors--when one uses the terms 'analytic' and 'synthetic', one must refer to judgments, what might today be called assertions--can be called 'analytic a posteriori'; synthetic a posteriori judgments, for their part, just are what Kant calls straightforwardly synthetic judgments, since they depend on experience.

But while it's not clear to me that your suggestion can be brought to bear on the particular case of the missing shade of blue, the notion of analytic a posteriori judgments is itself a very interesting one, which Kant himself was not able to envisage, but which may nevertheless constitute a category that merits some consideration. For consider an assertion such as 'Water is H2O'. This is a claim based on experience, but it's necessary. It can't, however, belong to the category of the synthetic a priori, at least as Kant conceives it, since synthetic a priori judgments are supposed to explain the possibility of experience, but not themselves to be objects of experience; the claim can't be analytic, since it's based on experience. So it might seem that, in virtue of its necessity and the fact that it is a claim about experience, that such a claim is best construed as 'analytic a priori'. If this is correct, however, what does this show about Kant's own division of judgments into analytic and synthetic? Might that not have to be rethought in much the same way that Kant himself may be taken to have rethought Hume's fork?