  What is the relation between perception and knowledge? Anaxagoras does not claim that perception alone is sufficient for knowing; nor does he seem to embrace skepticism. Sextus Empiricus, always on the lookout for arguments for and against any dogmatic position, gives us most of the evidence for Anaxagoras’ views. Says Sextus, of the skeptic’s methodology, “We set what is thought in opposition to what appears, as Anaxagoras set the appearance that snow is white in opposition to the claim that snow is frozen water, water is black, and therefore snow is black” (A97; but see the passage from Cicero in the same testimonium). Here Anaxagoras accepts that snow seems to us to be white, but claims that the reality must be that snow is black. The evidence of the senses must be corrected by what we know through thought. In B21, Anaxagoras recognizes the weakness of the senses (“Owing to feebleness [of the senses], we are not able to determine the truth”), but in B21a he accepts that sense perception can be a step towards understanding: “appearances are a sight of the unseen.” This follows from his own theory, for the evidence of our own control of our bodies by our minds, the facts of nutrition and growth, and the local revolutions of the heavens are evidence for the workings of cosmic nous, the No-Becoming principle, and the great cosmic revolution. Like other Presocratics, Anaxagoras leaves us with no detailed account of how knowledge derives from perception through the refinements of thought: Anaxagoras’ account can be compared with that of Democritus, where the relation of sense-perception and thought is similar and similarly unexplained.