Generations of playwrights and students have been taught that Aristotle laid down three strict rules for tragedy in his Poetics: a play must unfold in a single place, within a single day, following a single unbroken plot — the "three unities" of place, time, and action. It's a tidy rule, confidently attributed to a towering ancient authority. It's also not quite what Aristotle wrote.
What Aristotle actually said
In the Poetics, Aristotle analysed existing Greek tragedies — Sophocles above all — to describe common features of what made them work, and unity of action was the one he treated as genuinely essential: a tragedy should have one central, complete action, not a loose string of unrelated episodes stitched together. His remarks about time were closer to an observation than a rule — he noted that the tragedies of his era tended to unfold within roughly a single revolution of the sun, without insisting that future playwrights were bound to follow suit. About unity of place, he said essentially nothing prescriptive at all.
How an observation became dogma
The rigid, three-part version of the rule came later — much later. Italian Renaissance scholars rediscovering and translating the Poetics in the sixteenth century, and French neoclassical critics in the seventeenth, hardened Aristotle's descriptive comments into strict prescriptive law: a play, they insisted, must cover no more than twenty-four hours, occur in one location, and follow one unbroken line of plot, with any departure treated as a real breach of dramatic propriety. The dispute became famously public in 1637, when Pierre Corneille's play Le Cid was formally criticised by the French Academy, partly for violating unities that Aristotle himself had never actually demanded in the form his later champions insisted on.
What we're still unsure about
Exactly how much of the unity doctrine reflects Aristotle's genuine intent, versus later critical invention, is still debated among classicists — partly because the Poetics survives incomplete, with his planned companion treatment of comedy lost entirely, leaving scholars to reconstruct his fuller view from a partial and sometimes ambiguous text. How strictly even unity of action was meant to bind, and how far later readers over-systematised a working critic's working notes into a timeless rule, remains a live question in classical scholarship, not settled literary history.
This sits inside Greek Tragedy & the Aristotelian Unities, one of seven topics in Drama, one of five domains in Literature, one of seventeen subjects the app can quiz you on.