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.

16th century Italian and 17th century French critics expanded Aristotle's guidelines to make them into full rules for how a play must behave. English dramatists in the Elizabethan stage were largely unaware of these strictures. By the 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. Even Samuel Johnson was not free of applying the unities to drama when judging it in his Prefaces to Shakespeare.