Phantasia is the basic unit of Stoic psychology: an "impression in the ruling part," what presents itself to consciousness prior to any judgment upon it. Chrysippus defined φαντασία as τύπωσιν ἐν ψυχῇ — "an imprint upon the soul" (qualified: not a literal wax-tablet impression, but a pneumatic alteration). The Stoics divided φαντασίαι into (a) cognitive (καταληπτικαί) — those that carry the evidence of their own truth, and to which the sage alone gives assent, and (b) non-cognitive — all the rest, which must be approached with suspension of judgment (epochē). The φαντασία in itself is ethically neutral; ethical significance arises only when the TERMruling part gives or withholds assent (συγκατάθεσις) to it.

SVF I 53, 61–62 (Zeno); II 53–60 (Chrysippus); II 70–80, 87, 99 (the doctrine of καταληπτικὴ φαντασία); DL VII 45–54; LS 39, 40. In Marcus: Med. 2.5; 3.16; 5.16; 7.29 ("wipe out the impressions"); 8.7; 8.49 (the famous "add nothing of yourself to what the φαντασία announces"); 9.7; 11.19.

In 02-05 φαντασίαι are mentioned as the background from which one must "secure oneself a leisure" (σχολὴν … πορίζειν) — that is, not allow them to scatter attention away from the task at hand. Stoic attention is, first and foremost, work on φαντασίαι: separating the impression from the judgment one attaches to it. The famous Med. 8.49 — "add nothing of yourself to what the impression says" — is the condensed formula of epochē. Φαντασία binds together all three disciplines: assent (the κρίσις passed on an impression), desire (what seems good or bad to me), and action (impulse is born from assent). See TERMpathos — passion as false assent to an evaluative impression.