  Xenophanes’ most enduring philosophical contribution was arguably his pioneering exploration of the conditions under which human beings can achieve knowledge of the certain truth. The distinction between knowledge and true opinion set out in B34 quickly became an axiom of ancient Greek accounts of knowledge and survives in modern garb as the ‘belief’ and ‘truth’ conditions of the ‘standard’ or ‘tripartite analysis’ of knowledge. It can be plausibly argued that every later Greek thinker, at least until the time of Aristotle, undertook to respond to the basic challenge posed in Xenophanes’ B34—how, given the severely limited character of human experience, anyone can plausibly claim to have discovered the truth about matters lying beyond anyone’s capacity to observe first-hand. Xenophanes may also be credited with expanding the range of topics considered appropriate for philosophical inquiry and discussion. His Ionian predecessors had initiated the study of phenomena “above the heavens and below the earth” but, so far as we know, they did not turn their critical fire against the leading poets of ancient Greece nor did they seek through their teachings to correct or improve the conduct of their fellow citizens. Although many aspects of his thought remain the subject of scholarly debate, Xenophanes was clearly a multi-dimensional thinker who left his mark on many aspects of later Greek thought.