Suppose you are walking in the woods and come upon a mean-looking bear. The encounter scares the daylights out of you, and you begin to run for dear life. Do you run because you are afraid, or are you afraid because you run? The example and the question come from the work of William James, one of the first psychologists to propose a formal answer to questions about how autonomic responses are related to the experience of emotion. James argued that you are afraid because you run. Your running and other physiological responses, he said, follow directly from the perception of the bear. Without some form of these responses, you would feel no fear.

Presented like this, in its simplest form, James's theory may sound preposterous. It goes against common sense, which says that it would be silly to run from something unless you are already afraid of...