Within the depth-psychology and Hellenistic philosophy corpus, ‘impression’ (phantasia) occupies a foundational epistemological position, functioning as the primary interface between the external world and the perceiving soul. The Stoics, as elaborated by Long and Sedley and by Graver, treat impressions as physical affections of the psyche that simultaneously reveal their object and themselves — a self-luminous quality analogous to light. The central tension in the tradition turns on whether any impression can be certified as ‘cognitive’ (kataleptic), i.e., guaranteed to arise only from real objects as they truly are. Arcesilaus and the New Academy challenged this guarantee, insisting that every true impression has a false counterpart indistinguishable from it, inaugurating the suspension-of-judgement tradition. Carneades’ response — the ‘convincing’ impression as a practical criterion — marks a third major position. A further axis of debate concerns the structural role of impressions in action: the soul moves from impression through impulse to assent, and suppressing the last step does not dissolve the first two. Rudolf Otto mobilises a transformed sense of the term to argue that religious ‘impression’ requires an inner congeniality of spirit in the recipient, not mere sense-data. Freud’s work adds the dimension of childhood impressions as enduring psychic residues. The term thus spans ancient epistemology, Stoic action theory, sceptical epistemology, phenomenology of the sacred, and psychoanalytic memory theory.