This book, the writing of which was begun more than two years ago only to be interrupted for lengthy intervals, was originally planned as a short series of articles. I had no doubt at the time that sooner or later the whole behavioristic issue would be threshed out in book form, especially as the new movement in psychology had just about reached its peak in 1920. My own contribution to the discussion was to be merely the historical treatment and classification of the different species of behaviorism. Since, however, as I kept poring over the periodicals studying the ponderous articles with their animadversions on traditional psychology, the anticipated volume was not even promised, it occurred to me that the want might be filled through my own efforts.

That such a book is not out of season will be gathered from the recent letter of Prof. Hunter to the anti-behaviorists in which he asks" who are the behaviorists?" 1 and demands" a bibliography of this topic for the past decade." This exposition will perhaps convince him that there are more than two behaviorists, as he erroneously supposes, and