Which stylistic devices are used in The Crucible?

Arthur Miller, the author of the play, writes a sort of narrator for this work -- someone who interjects frequently in Act I -- to introduce characters, give the audience background information, etc.  We can call it authorial intrusion; the dialogue stops and this narrator steps in to tell us something it would be helpful to know, something the character is unlikely to reveal to us themselves: for example, John Proctor thinks he's "a fraud," Abigail Williams has an "endless capacity for dissembling," etc. 
Miller also makes heavy use of irony.  Dramatic irony is created when the audience knows more than a particular character, and it heightens tension and helps to build suspense.  For example, when Proctor, Francis Nurse, and Giles Corey come to the court in Act III to present their evidence against the girls and in favor of their wives (namely, the testimony of Mary Warren), Deputy Governor Danforth refuses to believe them; he says that the state believes "that the voice of Heaven is speaking through the children."  However, we know that Proctor is right: the girls are lying, but Dadnforth doesn't know this.  This is dramatic irony. 
It is also terribly ironic that Danforth refuses to believe Mary Warren, the only girl who is telling the truth, especially when he makes statements like, "We burn a hot fire here; it melts down all concealment."  On the contrary, the entire proceedings are founded on the deception of the girls!  This is an example of situational irony: the people who tell the truth are thought to be liars, and the liars are seen as truthful by the court.  We would expect the reverse -- that the truth will out, as they say -- especially in a court, but it is not so.