The purpose of evidence adduced in support of a theory is not to prove that theory true but to demonstrate that competing theories account for facts less well and thus no longer demand our attention. Evidence therefore, if it can unambiguously decide between competing theories, helps the discipline to spend its resources on only a few issues at a time. I evaluate this winnowing capacity of various kinds of evidence which have been offered in support of hypotheses on what knowledge native speakers' have about the sound patterns in their language and how they use it: surface sound patterns, sound change, poetry, speech errors, word games, and experiments. I argue that experiments provide evidence of the highest quality. Four experiments are reported, three psychological and one phonetic, which offer evidence on the following claims: (a) the psychological basis of speakers' awareness of phonotactics, (b) speakers' awareness of the morphemic constituents of complex derived words, (c) whether epenthetic stops of the sort evident in words like team[p]ster are added by purely mechanical constraints of the articulatory apparatus or whether they can be attributed to higher, pre-phonetic levels, and (d) the factors that determine speakers' assignment of allophones to phonemes.