The object of this book is to make the dynamics of the human mind intelligible to those who are more interested in understanding nature than in using big words or memorizing definitions. I have attempted to put ideas on a practical level which will give as clear and simple a picture as possible of complicated happenings. Long words have been avoided wherever this could be done without sounding clumsy. The object is to give the reader a better understanding of himself and others, and not to make a tea-room psychiatrist out of him. For those who want more details, the bibliographies should be an ample guide, and for those who want a technical vocabulary, a short glossary is appended.