 A famous quotation from Democritus distinguishes between perceived properties like colors and tastes, which exist only ‘by convention,’ in contrast to the reality, which is atoms and void. However, he apparently recognized an epistemological problem for an empiricist philosophy that nonetheless regards the objects of sense as unreal. In another famous quotation, the senses accuse the mind of overthrowing them, although mind is dependent on the senses. The accusation is that, by developing an atomist theory that undermines the basis for confidence in sense perception, thought has in effect undercut its own foundation on knowledge gained through the senses. Democritus sometimes seems to doubt or deny the possibility of knowledge.