"Nature" is one of the central concepts of the Stoic system, used in several senses: (1) the nature of the whole, identical with god-as-Logos and the cosmic order; (2) the nature of the human being — rationality and sociality; (3) the nature of a particular thing — its essential constitution. The Stoic imperative — "to live in agreement with nature" (ὁμολογουμένως τῇ φύσει ζῆν) — means simultaneously to follow the cosmic law and to realise one's own rational-social essence.

SVF I 179 (Zeno, the formula "to live according to nature"); III 4–9 (Chrysippus' development of the formula); DL VII 87–89; LS 63. In Marcus: Med. 2.1; 2.9; 2.16; 4.51; 5.3; 7.55; 10.6.

In 02-01 φύσις occurs three times: (1) "the nature of the good," (2) "the nature of evil," (3) "the nature of the one who errs." This triple invocation sets the structure of the whole passage: knowledge of three natures — the good, the bad, the human — frees us from the passions. The end of the passage returns to φύσις in negative form: "to act against one another is contrary to nature" (παρὰ φύσιν). The ethical norm is thereby derived from ontology: what breaks TERMcooperation also breaks the bond with the cosmos.