Three-act structure
The fundamental dramatic division: setup (act I), confrontation (act II), resolution (act III).
The three-act structure divides a story into setup (installing the world and triggering the conflict), confrontation (escalating obstacles) and resolution (climax and denouement). Inherited from Aristotle's Poetics — every story has a beginning, middle and end — and systematized by Hollywood dramaturgy, it's the implicit skeleton of the vast majority of Western narratives.
Its joints matter more than its blocks: the two pivots (the point of no return closing act I, the crisis opening act III) and the midpoint reversing the middle. The classic trap is act II's "sagging middle," twice as long as the others — all finer structures (Save the Cat, 7-point) were born to carve it up.
Example
Act I: the crime and the detective. Act II: false leads and escalation. Act III: confrontation and truth.