There is little more common in ethics than to think pain is intrinsically bad and pleasure is intrinsically good. A Humean-style error theory of the axiology of pain and pleasure is developed against these commonsense claims. We defend the thesis that the value of pain and pleasure is always contingent and only instrumental. We survey prominent theories of both intrinsic value and pain/pleasure, all of which assume that pain and pleasure are intrinsically valuable. We base our error theory on counterexamples (...) to this assumption, upon which these theories falter, and a theory of pain and pleasure which derives their value solely from their evolutionary function. (shrink)