“Act” comes from Latin actum, the nominalized passive past participle of agere, which means “to push ahead of oneself,” like the Greek agein [ἄγειν] ( cf. agôn [ἀγών], struggle, trial ); the Latin verb is differentiated, on the one hand, from ducere, “walk at the head of” ( like Gr. archêin [ἄϱχειν]; cf. PRINCIPLE ), and on the other hand from facere, “to do,” insofar as it implies duration, activity, and achievement rather than specific, instantaneous action ( thus agere aetatem, vitam, pass time, life ). Actus, the fact of moving, an action or the result of action, is a doublet of actio ( same etymology ), but the duality allows significant specializations: actus designates the action of a play ( which Aristotle designates by the words prattein [πϱάττειν] or pragmata [πϱάγματα] ) or its subdivision into acts, whereas actio is juridical and rhetorical ( court action, oratorical action, pleading ). Thus “actor” refers both to the character in a play and the person who plays that character: see ACTOR; cf. MIMÊSIS, PASSION.
The vocabulary of “act” is drawn from three great pairs of oppositions—ontological, ethical, and pragmatic—which constantly intersect with each other.
(BCDU)