A tragedy is a representation of an action that is whole and complete and of a certain magnitude. A whole is what has a beginning and middle and end.

A tragedy is the imitation of an action that is serious, and also, as having magnitude, complete in itself . . . with incidents arousing pity and terror, with which to accomplish its purgation of these emotions.

Tragedy is an imitation of a whole and complete action of some amplitude. . . . Now a whole is that which has a beginning, a middle, and an end.

The beginning, as the proverb says, is half the whole

... "you'd better go first or you'd better go last. No one will remember what come in the middle."
- "So what's the point of the middle than?" I asked. "If everyone only remembers the beginning and the end?"
-"Without the middle, being first or last means nothing."
The middle gave the rest its meaning.
Like life, maybe. People were born and then they died. Everyone remembers those events. But without the life in between...

Tragedy is thus a representation of an action that is worth serious attention, complete in itself and of some amplitude... by means of pity and fear bringing about the purgation of such emotions.