  In the Epicurean tradition the word ‘soul’ is sometimes used in the broad traditional way, as what animates living things (e.g., Diogenes of Oenoanda, fr. 37 Smith), but the focus of interest, so far as the soul is concerned, is very much on the mental functions of cognition, emotion and desire. A view that is common in the tradition and that very probably goes back to the founder is that the soul is a composite of two parts, one rational, the other nonrational. The rational part, which Lucretius calls mind [animus], is the origin of emotion and impulse, and it is also where (no doubt among other operations) concepts are applied and beliefs formed, and where evidence is assessed and inferences are made. The nonrational part of the soul, which in Lucretius is somewhat confusingly called soul [anima], is responsible for receiving sense-impressions, all of which are true according to Epicurus. Error arises at a later stage, when sense-impressions are interpreted by the rational part of the soul, in a way that, as we have seen, crucially involves memory. Sense-perception, conceived of simply as the reception of sense-impressions by the nonrational soul, does not involve memory (cf. L&amp;S 16B1). Since the formation and application of concepts requires memory, sense-perception, so conceived of, does not involve conceptualization, either. The nonrational part is also responsible for transmitting impulses originating from the rational part, as well as (presumably) for a wide variety of other vital functions. (When Epicurus distinguishes between pleasures and pains of the soul and those of the body, incidentally, the distinction he has in mind must be between the rational part of the soul on the one hand and the body animated by nonrational soul, on the other.) 