Starting in the 14th seminar of 1966-1967 … Lacan distinguishes between acting out and the act proper.
An act is an action that conjures into existence a signifying structure into which desire then, after the (f)act inscribes itself. The subject as a desiring being comes into existence in the wake of the act, instead of the act reflecting a previously present form of subjectivity. Lacan in the 14th seminar describes an act as a gesture of symbolization in which the subject is equivalent to the signifiers mobilized by this gesture; and he proceeds to add here that a shift of Symbolic surfaces occurs in a genuine act, that a “mutuation” of the subject transpires through such a deed … after passing through a “true act” the subject emerges transformed that this authentic gesture modifies the very configuration of subjectivity. Lacan,SXIV 2/15/67 . Johnston 147 Lacan,SXIV 2/15/67