In Act IV Danforth and the judges realize the court is in jeopardy. Rebecca Nurse, Martha Corey, and John Proctor are set to be executed because they will not confess to their crimes of witchcraft. Realizing that these are important people in Salem, Danforth knows it's important to get at least one of them to confess.
After talking with Hale and his wife, Elizabeth, John finally gives in and confesses. It looks like things are going to be okay for the courts. John will live, and they have a signed confession. Until John grows upset that they are planning to post his confession on the church doors.
Danforth asks Proctor
Is that document in your hand a lie? I will not accept it! I will not deal in lies Mister! You will give me your honest confession in my hand, or I cannot keep your from the rope.... Which way do you go Mister?
The irony in this statement is found in Danforth's belief that he doesn't "deal in lies" when the court's entire case has been built on the lies of the girls. All those who have confessed have lied. Proctor, by recanting his false confession (by tearing it up) is actually telling the truth, but Danforth will not listen to it.