κατόρθωμα (in Marcus also κατόρθωσις) is the "perfect," or "right," action: an act performed in accordance with complete TERMvirtue and right reason (ὀρθὸς λόγος). Etymologically from κατορθόω, "to set straight, to lead straight, to succeed"; hence the image of the straightness of the road (ὀρθότης τῆς ὁδοῦ).

The key distinction of Stoic ethics is between TERMκαθῆκον (the appropriate, "befitting" action) and κατόρθωμα (the perfect action). Their relation: every κατόρθωμα is a καθῆκον, but not conversely. A καθῆκον is defined by the content of the act (what it is reasonable to do — available even to the one still progressing, the προκόπτων); a κατόρθωμα is that same καθῆκον, but done out of a firm, unchanging virtuous disposition (διάθεσις). Hence κατορθώματα belong to the sage alone: they fully realise the end, whereas the "middle" καθήκοντα are only the right content without the perfection of the state.

SVF III 494–499, 500–543 (the doctrine of καθῆκον and κατόρθωμα); DL VII 108–110; Stob. Ecl. II 85–96 W; Cic. De fin. III 24, 58–59 and De off. I 8 (recte facta = κατορθώματα, officia media = καθήκοντα); LS 59. In Marcus: Med. 05-14 (κατορθώσεις as the straightness of reason's road).