Good therapists usually work to resolve conflicts, not inflame them. But there is a civil war going on in psychology, and not everyone is in the mood for healing. On one side are experts who argue that what therapists do in their consulting rooms should be backed by scientific studies proving its worth. On the other are those who say that the push for this evidence threatens the very things that make psychotherapy work in the first place. Which side prevails may shape not only how young therapists are trained and what techniques practitioners use in the future, but also...