 Plutarch argues that the crucial difference between the Platonic and the Stoic understanding of virtue is grounded in their different conceptions of soul as the source of human agency (De virtute morali 441C-E). While for the Stoics soul is reason only, Plutarch defends the conception of soul outlined in the Republic (esp. book 4), which presents the soul as consisting of rational and non-rational parts. As explained above (sect. 4), this fits well with Plutarch's interpretation of the creation of the world, according to which the pre-cosmic non-rational world soul is informed by the reason (logos) of the divine demiurge, yet this is not sufficient to eliminate its natural non-rationality. The non-rational aspect of the human soul accounts for emotions and bodily desires (Opsomer 1994, 41). In fact, however, Plutarch does not lump together bodily desires and emotions as constituting an undifferentiated non-rational part. Given the theory of Republic 4, Plutarch distinguishes spirit, as responsible for emotions, from appetite, which is responsible for bodily desires. But he classes them together to the extent that both are dependent upon reason, sensitive to, and nurtured by, it (De virtute morali 443C-D; Plat. Quest. 1008A-B). Plutarch describes virtue (without mentioning appetite) as the state in which reason succeeds in managing emotion and drives it in the right direction (De virtute morali 443B-D, 444B-C, 451C-E), while vice arises when emotion is not properly informed by reason (443D). Plutarch defines virtue as the state in which emotion is present as matter and reason as form (440D), a definition inspired by Nicomachean Ethics 1104b13–30 (cf. Aspasius, In Ethica Nicomachea 42.20–25). Plutarch's definition of virtue matches his account of how the world came into being, when matter was informed by reason. As with the world soul, similarly with the human soul in Plutarch's view, the impact of reason is possible because the soul, or part thereof, can heed what reason dictates.