The Renaissance came late to France, in part because of its civil war. When it did come, Cardinal Richelieu determined that theater would follow certain rules that conformed to a French neoclassical model. He established an academy that would decide whether a play deserved the label "neoclassical". Such a play had a strict form: it had to have five acts and be performed on a proscenium stage.
French neoclassicism had a strict sense of decorum that it expected its theater to adhere to. Kings should act like kings, servants should act like servants and everyone else should be strictly true to their roles in society. Everyone was expected to be mannerly and to behave in a morally upright fashion. If they didn't, then the play should, at some point, ensure that they were punished for their failure to exhibit proper decorum.
There could be no Hamlets or Macbeths in French neoclassicism theater as supernatural events were strictly forbidden. All action had to be believable and true to life. The French neoclassicists were early realists who would have found much in common with today's modern realism movement. French neoclassical plays could not demand too much suspension of disbelief on the part of its audiences.
Unity of Time
While the plays were all expected to be five acts long, they also had to take place in a 24-hour period. This sometimes led to absurdities such as the play "El Cid," in which an entire war takes place in 24 hours and the heroine marries her father's murderer hours after his death.
Unity of Place
All action had to occur in a single location. French neoclassical plays couldn't have any set or location changes. The academy occasionally allowed for loose interpretations of the single location rule, but it had to be logically justified.
Unity of Action
Forget subplots. The five-act plays of French neoclassical theater, modeled on ancient Roman theater, had to contain a single plot line. This allowed most theater companies to have companies of 12 actors who were "shareholders," with "pensioners" brought on when more were needed. Unlike in England, men and women were allowed to be on stage and be shareholders in the acting company.
Purity of Genre
Following classical ideals, French neoclassicism demanded that plays be either comedies of manners or heroic tragedies. These two genres were considered the only ones appropriate for the stage and the plays had to follow the rules of the genre.
Comedies had to have happy endings. Tragedies, on the other hand, had to end in death. Also, tragedies could not happen to common people. In the tradition of heroic tragedy, the hero had to be royalty or nobility. The lower and middle classes were appropriate subjects for comedy.
The phrase "poetic justice" had real meaning for the French neoclassicists and their dramatists. Characters in the play were expected to be dealt with according to their actions. The good were rewarded and the evil were punished. In doing so, the audience was enlightened, educated and entertained.