Hale is a dynamic character in this story and learns much about himself and society during his time in Salem. He comes to Salem with the arrogance of much intelligence, book learning, and some previous success. He makes an assumption about the behavior of the girls based on this knowledge of witchcraft, and does not hesitate before plowing forth with the "discovery" of the devil at work. His impetuousness is what causes events to get out of control.
In Act II, Hale has a long talk with the Proctors and slowly begins to understand that there is more to these townspeople than meets the eye. He sees that the Proctors are not immoral people, and is shocked when Elizabeth Proctor is taken. He has spent time with her individually, and can see that she is not possessed of the devil or of evil doing. The seed of doubt is planted.
However, it is the lack of legal proceedings in the court that really begins to change Hale's minds. As an educated and fair-minded man, he pleads with Danforth to take his time and get attorneys so that all the plaintiffs are represented in presenting their case against the list of townspeople. Danforth's refusal, and the power Abigail is demonstrating in court, convince Hale that this investigation has turned into a war.
Reverend Hale has become very upset over the number of people that have been hung or imprisoned as a result of his original findings. He believes that the Salem courts and the people of Salem have gone too far. Thus, he tries to help the Proctors, especially John, escape the death penalty. However, he is too weak morally to really question the decisions of the court and he never quite understands John Proctor's need to protect his name and reputation.