The Dogs and Cats Argument. Although a distinction between cats and dogs can be drawn, it turns out on closer examination to be a superficial one; it does not cut at the biological joints. Consider, for example, a paradigmatic cat, Felix. Felix has the following properties: (i) he has four legs, fur, and a tail; (ii) he eats canned food out of a bowl; (iii) humans like to stroke his back. Now consider a paradigmatic dog, Fido. Fido has all three of these properties as well. For instance, Fido also has four legs, and fur, and a tail, and when he eats, it is often served from a can into a bowl. And humans like to stroke Fido's back, too. In these respects, Fido and Felix are almost exactly similar. Therefore, there can't possibly be any deep biological distinction between them.I'm sure you'll agree that the dogs and cats argument is terrible. Put a pin in that and consider another argument.
In his contribution to Al Casullo and Josh Thurow's forthcoming volume, The A Priori in Philosophy, Timothy Williamson argues against the theoretical significance of the distinction between the a priori and a posteriori. The thesis of the paper is that "although a distinction between a priori and a posteriori knowledge (or justification) can be drawn, it is a superficial one, of little theoretical interest."
It's a somewhat puzzling paper, I think, because it's not at all clear how it's broad argumentative strategy is supposed to support the conclusion. Williamson does not, for instance, articulate what he takes the apriority distinction to be, then argue that it is theoretically uninteresting. Instead, he identifies certain paradigms of a priori and a posteriori knowledge, then emphasizes various similarities between them. For example, he argues that the cognitive mechanisms underwriting certain a priori judgments are similar in various respects to those that underwrite certain a posteriori judgments. Then he spends most of the rest of the paper arguing that these are not idiosyncratic features of his particular examples. But why is this supposed to be relevant?
The problem is obvious. As characterized above, the cognitive processes underlying Norman's clearly a priori knowledge of (1) and his clearly a posteriori knowledge of (2) are almost exactly similar. If so, how can there be a deep epistemological difference between them?But I do not find this problem at all obvious. The argument at least appears to have the structure of the terrible dogs and cats argument above. The thing to say about that argument is that identifying various similarities between two things does practically nothing to show that there aren't deep differences between them. There are deep biological distinctions between cats and dogs, but they're not ones that you can find by counting their legs or examining how humans interact with them. Similarly, Williamson offers nothing at all that I can see to rule out the possibility that there is a deep distinction between the a priori and a posteriori, but it is not one that is manifest in the cognitive mechanisms underwriting these judgments. For as Williamson himself later emphasizes, there's more to epistemology than cognitive mechanisms. If apriority lives in propositional justification—which is where I think it lives—then there's just no reason to expect it to show up at this psychological level. That doesn't mean it's not a deep distinction.
That Williamson's argument needs to be treated very carefully should also be evident from the fact that prima facie, it looks like it has enough teeth to show that the distinction between knowledge and false belief is not an epistemically deep one—a conclusion that everyone, but Williamson most of all, should reject. For the cognitive processes underlying cases of knowledge are often almost exactly similar to those underlying false beliefs. Should this tempt us to ask how, then, there could be a deep epistemological difference between them? I really don't see why.