In The Crucible, why doesn't John Proctor tell the court immediately what he knows concerning what has been happening ?
In Act II of The Crucible, we see Proctor at war with himself when challenged by his wife Elizabeth to tell the court what Abigail told him earlier: namely, that the witchcraft allegations are unfounded. Proctor hesitates to tell the court the truth, because this would hurt Abigail, expose her as a liar, and at this stage he still has feelings for her, as Elizabeth realises:
She has an arrow in you yet, John Proctor, and you know it well! (Act II)
Proctor therefore struggles to do what he knows to be the right thing. He does go to the court eventually, but only after his own wife Elizabeth is arrested, and he still hesitates to confront the court too openly. It all ends in disaster for him as his own affair with Abigail is revealed, destroying his credibility in the eyes of the Puritan court officials, and he too is accused of witchcraft.
Therefore, Proctor's personal entanglement with Abigail proves to be his undoing and destroys his good name. Ultimately, the only way out for him is death, which he chooses rather than falsely confessing to witchcraft. This, at least goes some way to redeeming him in his own eyes, atoning for his sin of adultery and his earlier hesitation to condemn the fear and falsehood of the court:
Now I do think I see some shred of goodness in John Proctor. Not enough to weave a banner with, but white enough to keep it from such dogs. (Act IV)
John Proctor has, appropriately enough, been utterly bewitched by Abigail Williams. And by the time we get to act 2, he's still very much in thrall to her seductive charms. For him to accuse her publicly of lying would not just get her into trouble; it would also expose their affair, which would constitute an open admission of his own wickedness in succumbing to the temptation of the devil. Despite his affair with Abigail, John still sees himself as a righteous Christian man. To implicate Abigail in the deliberate spreading of falsehoods would make him, in his own eyes and those of the community, both less of a Christian and less of a man.
John is also unbearably tormented by his own guilt complexes. He already feels guilty in himself and in the eyes of God. The last thing he wants is to be judged guilty by the community as well. The community, for good or ill, is John's whole life. His identity is completely bound up with the position he occupies within that community. At this stage in the play, John simply cannot see any other role that he can take on for himself. It is only later on that he will finally do so, adopting the role of martyr and so finally extinguishing the guilt that has so utterly paralyzed him.