I DO not expect this book to stand upon its literary merits; for if it is unsound in principle, felicity of diction cannot save it, and if sound, homeliness of expression cannot destroy it. My primary object in offering it to the public is to assist in bringing Psychology within the domain of the exact sciences. That this has never been accomplished is owing to the fact that no successful attempt has been made to formulate a working hypothesis sufficiently comprehensive to embrace all psychic phenomena. Sincerely believing in the correctness of my hypothesis, I have not hesitated to follow it to its legitimate conclusion in every field which I have entered. If at the close of the book I have seemed to trespass upon the forbidden field of theological discussion, it was not for the purpose of sustaining any preconceived opinions of my own; far from it. It was because I was irresistibly led to my conclusions by the terms of my hypothesis and the inflexible logic of its application. I cannot but be aware that my conclusions sometimes oppose the preconceived opinions of others. But no one who accepts my hypothesis as the true one will be compelled more frequently than I have been to renounce his former convictions.