The three-act structure is the form that I grew up in the theater with. You generally present a situation in Act I, and by the end of Act I the situation has evolved to a point where something is threatening the situation. In Act II you solve that problem producing a more intense problem by the end of Act II. In Act III you solve that problem, either happily or unhappily, depending on whether you have a comedy or a tragedy or a drama: you work out the final solution accordingly.

PADDY CHAYEFSKY