The unities of time, place, and action were derived from Aristotle's Poetics by an Italian theorist, Lodovico Castelvetro, in 1570.
In Poetics, Aristotle proposes the unities of time and action (unity of place isn't mentioned in Poetics) as guidelines rather than actual rules, which are based on what Aristotle observed in Greek tragic plays—not what he intended to impose on the writing of tragic plays. Castelvetro and French classical playwrights like Pierre Corneille, Jean Racine and Jean-Baptiste Poquelin (better known as Molière) interpreted these observations as requirements and adhered to these unities in their plays.
According to Castelvetro, the unity of time imposed a twenty-four hour time limit on the action of the play, the unity of place meant that the action of the play should occur in a single location, and the action of the play be restricted to a single, unified plot line:
Tragedy endeavors, as far as possible, to confine itself to a single revolution of the sun, or but...
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