Plots are either simple or complex, since the actions they represent are naturally of this twofold description. The action, proceeding in the way defined, as one continuous whole, I call simple, when the change in the hero’s fortunes takes place without Peripety or Discovery; and complex, when it involves one or the other, or both. These should each of them arise out of the structure of the Plot itself, so as to be the consequence, necessary or probable, of the antecedents. There is a great difference between a thing happening propter hoc and post hoc.
Poetics