Chara is the Stoic technical term for the sage's rational joy — a εὐπάθεια (right disposition of the soul) corresponding to TERMἡδονή (the passion of pleasure) in the matrix of normal states of the soul. The Stoics distinguish four cardinal passions (TERMπάθη) and three cardinal εὐπάθειαι:

A note on the asymmetry: there are only three εὐπάθειαι (instead of four), because λύπη has no rational correlate — the sage takes nothing in the present to be a genuine evil and so cannot rationally "grieve."

Chara is defined as εὔλογος ἔπαρσις — a "rational uplift" of the soul. It is a pneumatic movement of the same kind as TERMἡδονή (also an ἔπαρσις), but rational: an expansion of the pneuma in response to a correctly identified genuine good (TERMvirtue), and not to a falsely identified apparent good (the pleasures of the flesh, success, reputation).

Sub-species of χαρά (according to Chrysippus): τέρψις (delight), εὐφροσύνη (cheerfulness), εὐθυμία (good spirits).

SVF III 431–442 (the doctrine of the εὐπάθειαι); DL VII 115–116; Stob. Ecl. II 88, 90 W (definitions via ἔπαρσις / συστολή); Cic. Tusc. IV 12–14, IV 66–68; De fin. III 35; LS 65W. As a technical term, chara is rare in Marcus: Med. 9.6 (in the context of the virtuous life); 10.13.

Chara is conceptually central for dispelling a common misunderstanding of the Stoics. They are often charged with preaching "insensibility" (TERMἀπάθεια) — the rejection of all emotion. This is wrong: the Stoic sage has no TERMpassions (which are false evaluative assents), but he does have three rational affective states — the εὐπάθειαι, among them chara. The sage rejoices — but he rejoices in virtue (his own and another's), not in wealth, status, or the pleasures of the flesh. This joy is calm, steady, independent of circumstance — because its object (virtue) is entirely within his power (dichotomy-of-control).

See Seneca Ep. 23: "Quod gaudium hoc est? hilaritate vacat… animum laetum et fidentem" — "what sort of joy is this? It is without giddiness… a glad and confident mind." This is chara: the sage's quiet, settled disposition, the opposite of the noisy unstable TERMἡδονή.

In Marcus there is little explicit discussion of chara (he is more occupied with TERMpathos, especially thymos and λύπη), but the concept works in the background: "to live in accordance with nature" = to live in such a way that the rational affects take the place of the passions.