In this book there will be nothing said concerning metaphysical theories or philosophical hypotheses; instead, there will be a very strict adherence to the principles of psychology. There will be nothing said of ''spirit'' or "soul''; but very much said of "mind." There will be no speculation concerning the question of "what is the soul," or concerning "what becomes of the soul after the death of the body." These subjects, while highly important and interesting, belong to a different class of investigation, and are outside of the limits of the present inquiry. We shall not even enter into a discussion of the subject of "what is the mind"; instead, we shall confine our thought to the subject of "how does the mind work."
