The Three Unities or dramatic unities are descriptions of how plays should be written, according to Aristotle. However, Aristotle was writing after the golden age of Greek drama, and many Greek playwrights, notably Aeschylus, wrote plays that do not fit within these conventions. The unities were:

1. The Unity of Time: The play was to take place during a single day.
2. The Unity of Space: The play must take place in a single location.
3. The Unity of Action: All action within the play was to be directed towards a single overarching idea.

Although it is often believed that these conventions originated in Aristotle's Poetics, it was not until French neo-classical drama in the 17th century that all Three Unities were actually maintained. Aristotle had merely recommended that 'Action' should only consist of the main plot without subplots, and that 'Time' should represent action not extending beyond the length of one day. The Unity of Place was not mentioned at all.

Maintenance of the three unities was particularly important to the classical French dramas of Molière, Racine, and Corneille. They held sway until Victor Hugo's Ernani; one of the things that made that play so controversial at its nineteenth century debut was its violation of this rule of classicism.

See also: History of theater and Theatre technique

The classical unities are three rules for drama derived from Aristotle's Poetics. They are:

1. Unity of Action: a play should have one main action that it follows, with no or few subplots.
2. Unity of Place: a play should cover a single physical space and should not attempt to compress geography, nor should the stage represent more than one place.
3. Unity of Time: a play should represent an action that takes approximately the same amount of time as the play; years should not pass during the hours a play takes.

Aristotle's comments in Poetics were descriptive, rather than prescriptive, and were meant to describe tragedy, but 16th century Italian and 17th century French critics expanded Aristotle's guidelines to make them into full rules for how any play must behave. French drama of the 17th century, particularly that by Corneille, was highly regular, whereas the contemporary English dramatists in the Elizabethan stage were largely unaware of these strictures. By the later 17th century, however, English dramatists (under the influence of French criticism picked up during the Interregnum) began to assess their own plays according to these rules. Thus, John Dryden, among many others, compares the "irregular" Shakespeare with the "regular" Ben Jonson in his Essay of Dramatick Poesie. Alexander Pope criticizes the violation of the unities in his Dunciad. In the 1728 version of the poem, the goddess Dulness notes that "Time himself stands still at her command,/ Realms shift their place, and Ocean turns to land" (Dunciad 1728, I 69-70). Additionally, he notes a violation of unity of action, as tragedy and comedy were mixed. Even Samuel Johnson was not free of applying the unities to drama when judging it in his Prefaces to Shakespeare.

See also

• Theatre technique