John Proctor ironically forgets, "Thou shall not commit adultery" when asked to cite the 10 Commandments in front of the judges. It is ironic because it is the one commandment he has broken. At this point in the story, John's guilt over his transgressions keeps him from accepting responsibility for his actions. He is not ready to admit he sinned; he still feels he can logically reason with the judges and townspeople without revealing his guilt. He knows he will be persecuted for his sins, and therefore, maybe unconsciously or consciously "forgets" this commandment. Even though John's wife, Elizabeth, knows about his affair with Abigail, John is not ready for it to be common knowledge in the community because of the price he would pay for his sin as well as his guilt and shame.