For a three-act plot analysis, put on your screenwriter’s hat. Moviemakers know the formula well: at the end of Act One, the main character is drawn in completely to a conflict. During Act Two, she is farthest away from her goals. At the end of Act Three, the story is resolved.
Act I
Act I wraps up as Stephen leaves the Whitsuntide play in a tizzy (Chapter Two), thus ending the first period of his childhood, and launching his restless quest for identity.
Act II
Father Arnall’s brutal series of tirades about hell and Stephen’s consequent religious crisis (Chapters Three and Four) mark the end of Act II, as he begins his super-pious (and markedly unartistic) period.
Act III
With Stephen’s epiphany at the seaside at the end of Chapter Four, we see him finally find an answer to his questions of identity and self-knowledge, thus setting him on the path to… his ultimate destiny.