intellection, understanding
νόησις is the highest of the four states of the soul (παθήματα ψυχῆς) distinguished on the "Divided Line": εἰκασία and πίστις correspond to the visible, discursive thought (διάνοια) and νόησις to the intelligible (τὸ νοητόν); and νόησις itself belongs to its upper segment, where the pure Forms dwell (Resp. VI 511d–e). On this segment the soul (ψυχή) ascends from hypotheses (ὑποθέσεις) to the "unhypothetical first principle of all" (ἀνυπόθετον) — the Form of the Good — and from there, with pure intellect (νοῦς), surveys the Forms themselves, using no sensible images (Resp. VI 511b–c). νόησις differs from διάνοια in its mode of discourse: διάνοια starts from assumed hypotheses and leans on sensible likenesses, such as drawn geometrical figures, whereas νόησις is led by the dialectical word (λόγος) alone and proceeds to the Forms without any sensory support (Resp. VI 510c–511b; VII 533c–534a).
In this act νόησις is the fullness of knowledge (ἐπιστήμη) of the intelligible: what crowns the "Divided Line" in book VI is in book VII called outright ἐπιστήμη, while διάνοια remains merely discursive thought (Resp. VII 533d–534a). In the "Phaedo" νόησις is described as the soul's work once it has detached itself from the body, since only thus can one approach being-itself (Phaed. 65b–66a). νόησις is the soul's encounter with truth (ἀλήθεια) and the opposite of opinion (δόξα), which is held back by what becomes.