Perhaps also there are some necessary truths about mind, language, and perception after all, a compendium of superscientific truths awaiting discovery and dissemination by philosophers. If so, however, one would expect the same to be true of other subjects. For example, one would expect there to be a set of necessary truths about all possible living things; and another set about all possible stars and galaxies; and another set about all possible forms of matter; and so on. One would expect, that is, a significant compendium of a priori knowledge on almost every significant subject: space, time, motion, light, matter, planets, fire, cosmology, life, weather, medicine, and so forth. Given the thousands of years philosophers have had to penetrate these subjects, we might well ask in which books the apodictic fruits of so much a priori labour have been written down. Put thus bluntly, the question is embarrassing. There is no such accumulated compendium of important a priori truths on any of these topics. And this despite the fact that philosophers have been talking and theorizing with enthusiasm about all of them for over twenty-five centuries. Claims of necessary truth have regularly been made, but empirical refutation has been their most common fate. What has accumulated instead is a rich compendium of a posteriori knowledge, a compendium born of the continuing labours of various subdivisions of earlier philosophy, subdivisions now quite properly identified as sciences. It now seems silly to expect philosophical techniques to reveal important necessary truths about all possible planets, or all possible forms of matter, or all possible living things. But if it is just plain silly to expect this for planets, matter, and life, why should it be sound philosophy to expect it for language, mind, and perception?