Telos is one of the key words of Greek ethics. In Plato and Aristotle it is the final end of an activity, that for the sake of which everything else is done; what is valued for its own sake, not for the sake of any other end (Aristot. EN I 1–2). In Stoic orthodoxy telos occupies a system-defining position: the whole of ethics is built up through a definition of the telos of human life.

The canonical Stoic telos-formulae:

• Zeno: τὸ ὁμολογουμένως ζῆν — "to live in agreement [with reason]."
• Cleanthes: τὸ ὁμολογουμένως τῇ φύσει ζῆν — "to live in agreement with nature."
• Chrysippus: τὸ κατὰ τὴν τοῦ ὅλου φύσιν ζῆν, οὐδὲν πράττων ὧν ἀπαγορεύειν εἴωθεν ὁ νόμος ὁ κοινός, ὅσπερ ἐστὶν ὁ ὀρθὸς λόγος — "to live in accordance with the nature of the whole, doing nothing that the common law (which is the same as right reason) forbids."

This formula is the basis of the doctrine "to live according to nature"; see that card for fuller treatment.

The distinction between telos and skopos (according to Antipater of Tarsus, Stob. Ecl. II 76 W) is technical:

• τέλος = "to obtain everything that accords with nature"; the attainment, which depends in part on external circumstance;
• TERMσκοπός = "to do everything in my power to obtain what accords with nature"; the taking-aim, which is entirely up to me.

This subtlety removes a potential paradox: if telos includes the attainment (and the attainment is not entirely mine), can I secure for myself a successful life? Answer: moral worth lies in the aim (σκοπός), not in the hit (τέλος). See Cicero's famous image of the archer at De fin. III 22.

SVF I 179 (Zeno's formula); I 552 (Cleanthes); III 4–16 (Chrysippus' extensive corpus); Antipater Tars. apud Stob. Ecl. II 75–77 W (the classical definition of telos and its distinction from TERMσκοπός); DL VII 87–89; Cic. De fin. III 21, 26, 31; Acad. I 36; LS 63, 64. Aristotelian background: Eth. Nic. I 1–2, 7; Politics I 2 (the telos of the polis). In Marcus the term occurs at: Med. 2.16 (what it means to live κατὰ φύσιν); 11.4; 11.21 («ἑνὶ σκοπῷ» — "with one aim," implicitly telos); 12.20 (no action lacks reference to telos / skopos).

In the Aristotelian system telos grounds the final cause (αἰτία τελική) — one of the four causes (alongside the material, formal, and efficient). The Stoics are more materialist: they have no distinct causes; everything unfolds through a single immanent Logos. But telos as a directive concept is preserved: the cosmos moves toward a telos (the maintenance of rational order), and the individual human being toward a telos (to live according to his own rational nature).

The modern word "teleology" is the heir of this term; in the modern era Aristotle's final cause was banished from physics (Descartes, Newton) but survives in biology (the function of an organ) and in ethics (the moral end).

Connections with other Stoic concepts:

• TERMεὔροια βίου (the smooth flow of life) — the characterisation of a life that has reached its telos.
• TERMεὐδαιμονία (flourishing) — synonymous with telos in ordinary Greek ethical language; for the Stoics it is specified as εὔροια.
• TERMἀρετή — the only sufficient means of attaining the telos (see virtue-is-sufficient).
• TERMσκοπός — the operational correlate of telos (what we actually aim at in every action).

In Marcus the telos of rational beings is programmatically formulated in 02-16: τέλος δὲ λογικῶν ζῴων τὸ ἕπεσθαι τῷ τῆς πόλεως καὶ πολιτείας τῆς πρεσβυτάτης λόγῳ καὶ θεσμῷ — "the telos of rational beings is to follow the reason and law of the most ancient polity" (see cosmopolis).