Poetics (6.7-6.11)

And since tragedy represents action and is acted by living persons, who must of necessity have certain qualities of character and thought—for it is these which determine the quality of an action;

it follows then that it is the plot which represents the action. By plot I mean here the arrangement of the incidents: character is that which determines the quality of the agents, and thought appears wherever in the dialogue they put forward an argument or deliver an opinion.

Necessarily then every tragedy has six constituent parts, and on these its quality depends. These are plot, character, diction, thought, spectacle, and song.

Two of these are the means of representation: one is the manner: three are the objects represented.[*]

This list is exhaustive, and practically all the poets employ these elements, for every drama includes alike spectacle and character and plot and diction and song and thought.