 Empiricist sentiments are also found in the work of some early medical writers. These go beyond a simple defence of sense perception to express a suspicion of theories that go beyond what can be observed. We find, perhaps, a hint of this attitude in the work of Alcmaeon of Croton (fl. ca. 500 BCE), to whom the following fragment is attributed: “Concerning things unseen the gods see clearly, but so far as men may conjecture… ” (DK 24B1; Kirk, Raven, &amp; Schofield 1983: 339). It would be wrong to read a body of empiricist doctrine into so cryptic a remark. But it may indicate the beginning of a contrast, not only between what the gods know and men may know (a commonplace of ancient Greek thought), but between knowledge that can be obtained by observation and knowledge of “the unseen.” The limits of human knowledge, it suggests, are marked by the limits of what can be observed.