It is not surprising that paradoxes and puzzles play an important role in philosophy. They are in Peircean language irritations to doubt-stimulants to inquiry. They confront us with problematic situations. They are barriers to the flow of philosophizing. Quine has emphasized the importance of paradoxes in the title essay to his The Ways of Paradox.1 In a much later essay, 'Natural Kinds',2 the particular stimulants to Quine's own inquiry seem to be Hempel's 'Paradox of the Ravens', and Goodman's 'Paradox of the Grue Emeralds'. The prima facie straightforward notions of confirmation and positive evidence prove anything but tractable to philosophical explication. A theory is confirmed if the positive evidence for it is sufficient. One theory is more highly confirmed than another if the quality and/or quantity of its positive instances is superior to that of the other. This all goes smoothly. Of course we still need to explain notions like quality of positive instance itself, but we expect to have little difficulty. Hempel's paradox, however, leads to the conclusion that a red chair is positive evidence for the 'theoretical' claim that all ravens are black. Prima facie, we wish to reject this conclusion, but where does Hempel's argument go wrong? (o) All ravens are black is logically equivalent to (g) All non-black things are non-ravens. A red chair is a non-black non-raven and hence positive evidence for (/), but (/) is logically equivalent to (a). A red chair is thereby positive evidence for All ravens are black. We are faced with a number of options none of which is attractive intuitively. We may simply accept the paradoxical conclusion and move on to explicate the notion of quality of positive evidence. We may reject the principle that logically equivalent theories possess the same positive evidence. As a desperate last resort we may even question the logical equivalence of (a) and (/). The paradox forces us to make some hard choices. It is easy to see how it acts as a trigger to inquiry. The problematic situation cries out for resolution. Goodman's paradox is simply a different trigger. A green emerald is positive evidence for the theoretical claim (y) All emeralds are green. It is also positive evidence for the claim (8) All