The girls are on oath to tell the truth in court.how does their idea of the 'truth' differ from John Proctor's? Does Mary Warren tell the truth or is she merely frightened from Abigail? If you were Abigail could you defend your version of the truth?
In The Crucible, perception is reality. The truth is too dark and dirty to mention. Once the girls pretenses are validated by the court officials, they become reality. Therefore, the truth is invented, and shaped to suit the various needs of people in Salem. Abigail and the girls dancing and conjuring in the woods is at the heart of the problem, but it is how this situation is used to get back at people that causes the real trouble.
Abigail uses the situation to get rid of Elizabeth, or so she thinks. John Proctor gets himself into the middle of this because of his affair with Abigail, and her desire to get him back. His wife is a victim.
Once the girls pretend to see spirits, they are too afraid to admit that they were only pretending because the penalty for their deception could be very grave. Danforth says at one point that Mary Warren's neck could break, meaning that she could be hung, for making false statements to the court.
Their truth is not the same as John Proctor's...or even Abigail's. She knows what the truth is, but she chooses to protect her own neck. She tells John Proctor what the truth is, but then she forces the girls to tell another version of the truth...one that I believe they actually see as the truth. With the exception of Mary Warren, the girls are scared to death of Abigail and what she SAYS is true in court IS true for them.
I don't think it's so much a matter of the girls' idea of truth differing from that of others, i.e., John Proctor; I think the bigger issue at hand is their incentive for telling the truth or for lying. There is much for them to lose if they tell the truth at this point, which is basically that they have lied and falsely accused many innocent people for their own selfish and vengeful reasons. Mary Warren's actions are all on account of fright; at first she agrees that she will tell the truth when John threatens to beat her if she does not, so she does so out of fear. Then, however, she ends up lying because her fear of what Abigail can do to her in court is greater than her fear of John.
I don't think Abigail is able to defend her version of the truth, primarily because it's not true at all. However, I don't think it even truly matters because those who are believed by the courts are the ones who are lying, so really Abigail does not need to defend her truth to anyone.