=284.= The Stoic psychology is in its fundamental principles wholly distinct from that of Plato; which does not at all prevent its exponents, and least of all those like Panaetius and Posidonius who were admirers of Plato, from making use of his system as an auxiliary to their own. Plato divided the soul into three parts; the rational part, the emotional (and volitional) part, and the appetitive[91]. Both the two latter parts need the control of the reason, but the emotional part inclines to virtue, the appetitive to vice[92]. The rational part, as with the Stoics, is peculiar to man; the other two are also possessed by the animals, and the appetitive soul even by plants. The Stoics do not however seriously allow any kinship between virtue and the emotions, and they deal with this part of the subject as follows. Nature has implanted in all living things certain impulses which are directed towards some object. An impulse towards an object is called ‘appetite’ (ὁρμή, _appetitus_ or _impetus_); an impulse to avoid an object is called ‘aversion’ (ἀφορμή, _alienatio_)[93]. In man appetite should be governed by reason; if this is so, it becomes ‘reasonable desire’ (ὄρεξις εὔλογος, _recta appetitio_)[94]; if otherwise, it becomes ‘unreasonable desire’ (ὄρεξις ἀπειθὴς λόγῳ) or ‘concupiscence’ (ἐπιθυμία, _libido_). To living things lower in the scale than man terms that are related to reason can of course not apply. [Sidenote: Will and responsibility.] =285.= Practical choice is, according to the Stoics, exactly analogous to intellectual decision. Just as the powers of sensation never deceive us[95], so also the impulses are never in themselves irrational[96]. An impulse is an adumbration of a course of action as proper to be pursued[97]; to this the will gives or refuses its assent[98]. It is the will, and the will only, which is liable to error, and this through want of proper tone and self-control. If there is this want, it appears in a false judgment, a weak assent, an exaggerated impulse; and this is what we call in ethics a perturbation[99]. A healthy assent leads up to a right action: a false assent to a blunder or sin. Hence we hold to the Socratic paradox that ‘no one sins willingly’ (οὐδεὶς ἑκὼν ἁμαρτάνει); for the true and natural will cannot sin; it must first be warped to a false judgment and weakened by slackness of tone. We can equally use the paradox that ‘every voluntary action is a judgment of the intellect,’ or (in few words) that ‘virtue is wisdom’ (φρόνησις ἡ ἀρετή). In such views we find a starting-point for dealing with the problems of ethics, including those of the ethical ideal or supreme good, its application to daily duties, and its failure through ignorance or weakness of soul. [Sidenote: The body.]