SUCH a book as this is almost inevitably bad; in the sense at least that what the reader will find will not correspond to what he hopes for or expects. Things in which he is little interested will be treated at apparently unnecessary length and with unreasonable emphasis; while other aspects of the subject, on which he would willingly linger, are summarily dismissed or omitted altogether. No doubt this happens to some extent in any historical treatment of a branch of knowledge. In the case of psychology itself, one of the most balanced and comprehensive of the several excellent histories that have been written in recent years speaks of its own "strange silences and vast lacunæ". I fear that in the present volume, which is deliberately constructed on more impressionistic and less systematic lines, such faults will appear even more glaring and outrageous.
Nevertheless something can often be learnt even from a bad book--if only through the arousal of a critical attitude which will help the reader to seek out the author's omissions, discount his prejudices and correct the shortness of his vision; and I hope that the following pages will at least have this much salutary influence. I believe moreover that any student of a science (even the beginner) will do well to supplement his textbook by a treatment of his subject from the developmental point of view; since the value to be obtained from the study of a science lies, not merely in an understanding of the relevant facts and principles, but also in a contemplation of the struggle of the human mind with the peculiar problems of the science; and in a realization of how our present