Telos

Telos is the ancient Greek term for an end, fulfilment, completion, goal or aim; it is the source of the modern word ‘teleology’. In Greek philosophy the term plays two important and interrelated roles, in ethics and in natural science; both are connected to the most common definitional account of the telos, according to which a telos is that for the sake of which something is done or occurs.

In ethical theory, each human action is taken to be directed towards some telos (i.e. end), and practical deliberation involves specifying the concrete steps needed to attain that telos. An agent’s life as a whole can also be understood as aimed at the attainment of the agent’s overall telos, here in the sense of their final end or summum bonum (‘highest good’), generally identified in antiquity as eudaimonia (happiness). Rival ancient ethical theories are distinguished primarily by their rival specifications of the end; the Epicurean telos is pleasure, the Stoic telos is life according to nature, and so on.

In the natural science of Aristotle, the telos of a member of a species is the complete and perfect state of that entity in which it can reproduce itself (so, insects reach their telos when they become adults). The telos of an organ or capacity is the function it plays in the organism as a whole, or what it is for the sake of; the telos of the eye is seeing. Carrying on the tradition of Anaxagoras and Plato, Aristotle centres his scientific methodology around the claim that there are ends in nature, i.e. that some natural phenomena occur for the sake of something; Galen and the Stoics enthusiastically second this; Epicurus rejects it.