Classicism

Classicism, in the arts, refers generally to a high regard for classical antiquity as setting standards for taste which the classicist seeks to emulate. Classicism is usually contrasted with romanticism; the art of classicism typically seeks to be formal, restrained, and Apollonian rather than Dionysiac, in Friedrich Nietzsche's well known opposition.

In the theatre

Classicism in the theatre was developed by 17th century French playwrights from what they judged to be the rules of Greek classical theatre, including the Three Unities of time, place and action.

Unity of time referred to the need for the entire action of the play to take place in a fictional 24-hour period
Unity of place was as it sounds, the action had to unfold in a single location
Unity of action meant that the play should be constructed around a single 'plot-line' , such as a tragic love affair or a conflict between honour and duty.

The language also had to be of the most exalted kind, excluding 'low-life' characters and smutty jokes.

Classicists did not approve of Shakespeare, who broke all these rules and plenty more.

Examples of classicist playwrights:

Victor Hugo was among the first french playwrights to break these conventions.