Epicurus invented the term canonic to designate epistemology as a branch of philosophy. This chapter deals first with perceptions and feelings, then preconceptions. Turning first to sight and thought to explain sensory perception, Epicurus claims that very fine configurations of atoms, called images, are continually detached from the surface of external solids, having similar shape and colour to the solid. Epicurus does not explain feelings separately in the Letter to Herodotus. Their epistemological role can be inferred, however, from what he says about perceptions. The basic difference between these two measures of truth is that feelings are acts of awareness of inner states, whereas perceptions are directed at what is external to us. Preconceptions correspond to the utterances used to state a belief or problem. Beliefs are of two kinds: about what is waiting and about what is nonevident. The senses can display the things that we believe to exist.