  Only a few fragments and testimonia discuss Anaxagoras’ views on perception and knowledge in living things. Aristotle and Theophrastus give us some account of his theory of perception, saying, most surprisingly, that for Anaxagoras all sensation is accompanied by discomfort or pain (A92). Theophrastus links this to Anaxagoras’ belief that like is perceived by unlike; on Theophrastus’ view, perception is via touch, and unlike things produce some irritation when touched. Theophrastus adduces loud noises and very bright light as producers of pain in perceivers, and suggests that the mechanism is the same in all cases of sensation. Some irritation will be below the level of awareness for most perceivers, which is why humans do not normally feel pain when perceiving (see Warren 2007 for a good discussion of Anaxagoras on perception).