Kathēkon (Greek: καθῆκον) (plural: kathēkonta Greek: καθήκοντα) is a Greek concept, forged by the founder of Stoicism, Zeno of Citium. It may be translated as “appropriate behaviour”, “befitting actions,” or “convenient action for nature”, or also “proper function.” Kathekon has been translated in Latin by Cicero as officium, and by Seneca as convenentia. Kathēkonta are contrasted, in Stoic moral, with katorthōma (κατόρθωμα; plural: katorthōmata), roughly “perfect action.” According to Stoic philosophy, man (and all living beings) must act in accordance with Nature, which is the primary sense of kathēkon.
1 Kathēkonta and katorthōmata
2 Indifferent things
3 Intentionality and perfection
Kathēkonta and katorthōmata
According to Stoic philosophy, each being, whether animate or inanimate (plant, animal or human being), carries on fitting actions corresponding to its own nature. They distinguished between “kathēkonta” and “katorthōmata,” a perfect action derived from the “orthos logos” (reason) (also “teleion kathēkon”: a perfect, achieved kathēkon). They said that the wise man necessarily carried out katorthōmata, that is, virtuous kathēkon, and that what distinguished both was not the nature of the act, but the way it was done. Thus, in exceptional circumstances, a wise man (which state of being, in Stoic philosophy, is nearly impossible to achieve) could carry out a katorthōma which, according to ordinary standards, would be deemed monstruous (for example, having sexual intercourse with one’s daughter, if the destiny of humanity is at stake, or mutilating oneself).
Stoic morality is complex, and has various hierarchical levels. On the first, lay-man level, one must carry out the action corresponding to his own nature. But, according to the Stoic strict moral ideas, the acts of laymen are always insane (ἁμαρτήματα hamartēmata  “mistakes,” or peccata), while the acts of the rare wise-man are always katorthōmata, perfect actions. The wise man acts in view of the good, while the ordinary being (layman, animal or plant) acts only in view of its survival. However, both act according to their own nature.
Stoic philosophers distinguished another, intermediary level between kathēkonta and katorthōmata: mesa kathēkonta, or indifferent actions (which are neither appropriate, nor good). A list of kathēkonta would incl