Nous is most likely derived from the root snu, meaning "to sniff." Homer uses nous to mark the realization or understanding of a situation or state of affairs. Nous penetrates beyond the surface features of a situation and reveals the underlying truth of the matter. It is not divorced from perception and its most primitive function is that of apprehending or "smelling" danger. In Homer nous is also linked to the visualization of a plan of action that is immediately prompted by the awareness of a situation possessing emotional impact.
In Parmenides nous maintains its Homeric function as that which reveals ultimate truth. However, it also serves as the source of logical reasoning. In Parmenides nous is divorced from perception and it is best understood to mean "thought" or "intellect." In accordance with his rather austere ontology, Parmenides may well hold that that which exists is also that which thinks (i.e., no thing that exists fails to be a thing that thinks).
Anaxagoras treats nous as a mass term, like water or air (as opposed to a count term, like man or leaf). He appears to treat nous, not as "intellect," but as "reason" or "the virtue of rationality." Nous, for Anaxagoras, is the ultimate source of order and motion in the cosmos. By both initiating and governing a vortex, nous brings order to an otherwise static primordial chaos. Anaxagoras asserts that nous is the lightest and purest thing. In so doing, he may well be attempting to articulate the idea that nous is an immaterial substance.
Plato incorporates elements from Parmenides, Homer, and Anaxagoras into his treatment of nous. First, following Parmenides, Plato considers nous to be an intellectual faculty that is wholly divorced from perception. Second, following Homer, Plato considers nous to be a source of insight or intuition. Still, for Plato, intuition is a nonempirically based grasp of unchanging and eternal truth. Finally, following Anaxagoras, Plato considers nous to be the source of order and motion in the cosmos. Nous, as rationality itself, is the substance that orders the heavens for the sake of the best. It is the cause of regular celestial motion and it is the cause of rationality in humans.
Aristotle, in his treatment of nous, displays acute awareness of views advanced by his predecessors. First, Aristotle takes nous to be a source of insight. Nous is a grasp of the salient features of a situation, but it is also a grasp of universal scientific principles. Nous, even in its later role, is not divorced from perception. It is the grasp of principles that are acquired by induction from perceived cases. Second, Aristotle uses nous to mean "intellect." He asserts that one's nous is separate from the body. In so doing, Aristotle is likely to be advancing the view that human intellect is an immaterial faculty. Finally, Aristotle's God, the Prime Mover, is nous. It is a separately existing and fully actualized rationality. This nous is the chief cause of motion, order, and goodness in the cosmos.
Lesher, James H. "The Meaning of Nous in the Posterior Analytics." Phronesis 18 (1973): 44–68.
Menn, Stephen. Plato on God as Nous. Carbondale: Southern Illinois University Press, 1995.
Von Fritz, Kurt. "Noos and Noein in the Homeric Poems." Classical Philology 38 (1943): 79–93.
Von Fritz, Kurt. "Nous, Noein, and Their Derivatives in Pre-Socratic Philosophy (excluding Anaxagoras)." Classical Philology 40 (1945): 223–242 and 41 (1946): 12–34.
John E. Sisko (2005)