E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Dramatic Unities (The thrée).
One catastrophe, one locality, one day. These are Aristotles rules for tragedy, and the French plays strictly follow them.
The French have added a fourth, one style. Hence comedy must not be mixed with tragedy. Addisons Cato is a good example. Unity of style is called the Unity of Uniformity. Shakespeare disregards all these canons.