This chapter shows that the sceptical empiricist argument, and by extension any argument like it, fails. It considers the concept of evidence, endorsing Williamson's view that all and only knowledge is evidence, (E=K). In particular, it considers the alternative view that only observational knowledge is evidence. Bas van Fraassen's constructive empiricism is then studied. Some commentators employ a caricature of constructive empiricism that takes the same argument. In fact, van Fraassen is careful to distance himself from scepticism about theories and to take constructive empiricism to be a view about the aim of science. It is argued that van Fraassen ought to be committed to the sceptical conclusion, and that constructive empiricism is implicitly committed to the above argument.
Keywords: constructive empiricism, Williamson, underdetermination, observable knowledge, epistmic scepticism, sceptical empiricist argument