individual mind alone that appeal is made, and this is what Protagoras asks for. "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.