As supposed events being accessible to a unique observer, private events posit an interesting challenge to a behavioristic psychology. Three historical variants of behaviorism dealt with the problem of private events: methodological behaviorism, radical behaviorism and interbehaviorism. The basic argument of the two last views, and that distinguishes them from the former, is that private events are comprised into the scope of an objective science of behavior. The analysis of these accounts permits us to confirm a gradual advance in behavior theory, in dealing with this issue, toward a totally monistic view.