soul, life
The soul (ψυχή) — for Plato, the principle of life, motion, and cognition, prior to the body (σῶμα) and more akin to the intelligible than to the sensible. In the Phaedrus the soul is defined as self-moving (τὸ αὐτὸ κινοῦν) and therefore an eternal, immortal beginning: "all soul is immortal, for what is ever in motion is immortal" (Phaedr. 245c). In the Laws it is called the source of all motion and prior to the body (Leg. X 896a), and in the Phaedo it is shown that the soul brings life with it and does not admit death (Phd. 105d). Hence Plato's conception of philosophy as "care of the soul" (ἐπιμέλεια ψυχῆς) and as a practice for dying — a purification (κάθαρσις) of the soul from the power of the body and the sensual passions (Phd. 64c–67b).
In the Republic the soul is shown to be tripartite: the rational part (λογιστικόν), the spirited part (θυμοειδές), and the appetitive part (ἐπιθυμητικόν), justice (δικαιοσύνη) in the soul consisting in the accord of these parts under the rule of reason (Resp. IV 435b–441c). But this tripartition belongs to the soul as joined with the body; its true nature is disclosed only when the soul is contemplated "in itself" (καθ' αὑτήν), beyond the bodily accretions (Resp. X 611b–612a). In the Timaeus the notion of soul is extended to the cosmos as well: the world-soul is fashioned by the demiurge out of the same and the different and makes the whole cosmos living and rational (Tim. 34b–37c).
It is to the circle of logos that the soul is most closely bound: it is in the soul that λόγος unfolds, for thinking (διάνοια) is, in Plato's words, "the silent speech that the soul carries on with itself" (Tht. 189e–190a). In the soul there dwell knowledge (ἐπιστήμη), opinion (δόξα), and intellect (νοῦς) as its highest power; the ascent toward truth (ἀλήθεια) is the turning of the whole soul from becoming to what truly is (Resp. VII 518c). The supporting connections of psyche are logos (λόγος), intellect (νοῦς), knowledge (ἐπιστήμη), opinion (δόξα), body (σῶμα), immortality (ἀθανασία), virtue (ἀρετή); the soul is opposed to the body as the immortal to the mortal and as the self-moving to what is moved from without.