The Three Unities
These unities, proposed by Aristotle and imitated by the Neoclassicist included time, place, and action.
Unity of Time (suggested in 1543) means that the events of the play must occur within one day. According to the Neoclassicists, audiences cannot believe that years pass in the course of a performance.
Unity of Place (in 1570) means that the scenes of the play must occur in the same location.
Unity of Action, suggested by the Greeks, means that only one major plot can be performed in the course of a play.
Lodovico Castelvetro (1501-1571) is the writer who states, in 1570, that these three rules must be followed in all plays.