Telos (from the Greek τέλος) — “end,” “purpose,” “goal,” or “completeness”: that for the sake of which something exists, develops, or acts. The word names not so much a final point in time as the full realization of a thing’s nature, the state in which it attains its proper perfection. It is one of the central concepts in Aristotle’s philosophy, for whom the telos corresponds to the final cause, one of the four causes that explain why something is as it is. To understand a thing, on this view, is to grasp what it tends toward: the seed tends to become a tree, and the eye exists for the sake of seeing. Explanation by ends is called teleology. In ethics, Aristotle holds that each being has a proper function (ergon) and that the telos of the human being is eudaimonia — the fully realized life lived in accordance with reason and virtue. The telos is here distinguished from the mere efficient cause, which accounts for what sets something in motion rather than for that for the sake of which the motion occurs. In the modern period, Kant questions whether nature can be explained teleologically in a strict sense, since this would seem to ascribe intention to it; he nonetheless admits teleology as a regulative principle, useful for thinking of living organisms as if they were ordered toward ends. Darwinism, by contrast, dispenses with intrinsic purpose, replacing the telos with variation and natural selection. The concept remains decisive in debates over purpose, function, and meaning in nature and in human action.
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