In The Crucible by Arthur Miller, what is the effect of verbal, situational, and dramatic irony?

As is the case with most irony, situational and dramatic irony is used in The Crucibleto increase tension and heighten suspense.  First, the situational irony of having children calling the shots in the witch trials undermines the authority of adults who should and do know better, and it increases tension for readers because these children are essentially in charge of who lives and who dies in Salem.  As Proctor says, "now the little crazy...

As is the case with most irony, situational and dramatic irony is used in The Crucible to increase tension and heighten suspense.  First, the situational irony of having children calling the shots in the witch trials undermines the authority of adults who should and do know better, and it increases tension for readers because these children are essentially in charge of who lives and who dies in Salem.  As Proctor says, "now the little crazy children are jangling the keys of the kingdom [...]!"  The children's accusations overwhelm common sense, reputation, trust, everything that has always mattered.  That so much faith is put into the words of children, children who are fickle, easily manipulated, or often lie, creates irony of situation because it should be reasonable, unemotional, objective adults who are in charge of life or death scenarios (if anyone must be). 

Dramatic irony also increases tension for the audience, building up to the climax of the play.  Parris and the Putnams know that Abigail and the girls were conjuring spirits in the woods, but they keep this information from the magistrates until it is forced out during Act III.  Proctor and Abigail know that they've had an affair, but they keep this from the magistrates until John accuses Abigail of lying; Elizabeth knows too, but she tries to hide the information in an effort to save her husband's reputation (an attempt which, ironically, completely undermines Danforth's willingness to believe John).  Abigail told Proctor that Betty only "took fright" when her father jumped out of the woods and scared her, and that her illness has nothing to do with being witched, but he keeps this from the magistrates for two weeks.  However, we know all these things, and the audience, alone, has all the information -- information that so many characters seek to hide from so many others -- and this heightens tension for us, increasing our suspense and making the story that much more compelling and tragic because we can see how miscommunications, misunderstandings, and well-intentioned attempts to protect someone else result in dire consequences.