Quotation by Northrop Frye

A tragic or comic plot is not a straight line: it is a parabola following the shapes of the mouths on the conventional masks. Comedy has a U-shaped plot, with the action sinking into deep and often potentially tragic complications, and then suddenly turning upward into a happy ending. Tragedy has an inverted U, with the action rising in crisis to a peripety and then plunging downward to a catastrophe through a series of recognitions, usually of the inevitable consequences of previous acts. But in both cases what is recognized is seldom anything new; it is something which has been there all along, and which, by its reappearance or manifestation, brings the end into line with the beginning.