"We thus find, in Plato's philosophical character, two extreme opposite tendencies and opposite poles co-existent. We must recognize them both, but they can never be reconciled; sometimes he obeys and follows the one, sometimes the other.
"If it had been Plato's purpose to proclaim and impose upon every one something which he called 'Absolute Truth,' one and the same alike imperative upon all, he would best proclaim it by preaching or writing. To modify this 'Absolute,' according to the varieties of the persons addressed, would divest it of its intrinsic attribute and excellence. If you pretend to deal with an Absolute, you must turn away your eyes from all diversity of apprehending intellects and believing subjects."
With such testimony to the value of dialectic debate, I hope that my adoption of it as a method will be regarded as something better than an affectation.
Mr. Spencer, in one of his works,[1] referring to and quoting from Berkeley's "Dialogues of Hylas and Philolaus," observes that "imaginary conversation affords great facilities for gaining a victory. When you can put into an adversary's mouth just such replies as suit your purpose, there is little difficulty in reaching the desired conclusion." I have not written to gain a victory; and, indeed, I am quite aware that it would be impossible to gain one over those with whom I can have no common ground of reasoning. In the imaginary conversations in this work, I have taken great care not to put into the mouth of the supposed representative of the doctrine of evolution anything that would suit my own purpose; and, in every instance in which I have represented him as relying on the authority of Mr. Darwin or of Mr. Spencer, I have either made him quote the words or have made him state the positions as I suppose they must be understood, and have referred the reader to the proper page in the works of those writers.
And here I will render all honor to the admirable candor with which Mr. Darwin discussed objections to his theory which have been propounded by others, and suggested further difficulties himself. If I do not pay the same tribute to Mr. Spencer, the reason will be found in those portions of my work in which I have had occasion to call in question his methods of reasoning.
Some repetition of facts and arguments will be found in the following pages in the different aspects in which the subject is treated. This has been intentional. When the tribunal that is addressed is a limited and special one, and is composed of a high order of minds accustomed to deal with such a science, for example, as jurisprudence, he who undertakes to produce conviction can afford to use condensation. He seldom has to repeat what he has once said; and often, the more compact his argument, the more likely it will be to command assent if it is clear as well as close. But this work is not addressed to such a tribunal. It is written for various classes of readers, some of whom have already a special acquaintance with the subject, some of whom have less, and some of whom have now none at all. It is designed to explain what the theory of evolution is, and to encounter it in the mode best adapted to reach the various minds of which the mass of readers is composed. If I had written only for scientists and philosophers, I should not have repeated anything.
For similar reasons I have added to this volume both a general index and a glossary of the scientific and technical terms which I have had occasion to use.
The whole of the text of this work had been written and electrotyped before I had an opportunity to see the very interesting "Life and Correspondence" of the illustrious naturalist, the late Louis Agassiz, edited by his accomplished widow, Mrs. Elizabeth Cary Agassiz, and published in October, 1885, by Houghton, Mifflin and Company, Boston. For a long period of years, after his residence in this country began, and until my removal from Boston to New York in 1862, I enjoyed as much of his intimacy as would be likely to subsist between persons of such different pursuits. I believe that I understood his general views of creation, from his lectures and conversation. It is now made entirely certain that he never accepted the doctrine of evolution of distinct types out of preceding and different types by ordinary generation; and it has been to me an inexpressible satisfaction to find that the opinions and reasoning contained in my work, and adopted independently of any influence of his, are confirmed by what has now been given to the world. I need only refer to his letter to Prof. Sedgwick, written in June, 1845, and to his latest utterance, the paper on "Evolution and Permanence of Type," in the thirty-third volume of the "Atlantic Monthly," published after his lamented death in 1873, for proof that his opinions on the Darwinian theory never changed. Of all the scientists whom I have ever known, or whose writings I have read, Agassiz always seemed to me the broadest as well as the most exact and logical reasoner.
New York, September, 1886.