By some even modern thinkers Intuition is boldly claimed to be an instrument of research; by others its very existence, outside of morbid imagination, is denied, and the only legitimate instrument of research is declared to be observation verified by experiment that can be repeated at will. The truth, as usual in controversy, includes both statements, and is covered by neither. Creatures with rudimentary eyes and ears must have "intuitions" of colors and sounds beyond their capacity of clear apprehension; and even our eyes, which must be rudimentary compared with possible eyes, have in regard to even our spectrum, intuitions, some of which have recently been made clearer by the photograph and the X-ray. These cleared-up intuitions are now added to positive knowledge. Intuition is here proved an instrument of research, and it is one in every discovery. But until verified by experiment, it is not a _reliable_ instrument of research: for what seems to be intuition is often mistaken, and is generally so vague as to be subject of conflicting opinions, and hence of conflicting action. Moreover, as the subjects of intuition are beyond our knowledge, intuitions are often held to be superior to knowledge, and worthy of greater enthusiasm. Consequently conflicting opinions regarding intuitions have probably led to more tragedies than any other blunder. There is no intuition more nearly universal than that of the immortality of the soul. But even so devout a man as Fiske pronounced it unverifiable, and it is so uncertain that all sorts of conflicting dogmas have grown up around it, until it has led not only to the self-immolations of India and the human sacrifices of Mexico, but to the Arena of Nero, the inquisition of Torquemada, the Thirty Years' War, and even within the memory of living men, the agonizing rupture of many a family. Fiske did more, through deductions from the law of Evolution, toward putting this most important of intuitions upon the basis of established knowledge, than any man had done before him. He did this not only in his writings on _The Idea of God_, _Through Nature to God_, and _The Destiny of Man_, but in the whole tendency of his work, not only when expounding the Law of Evolution as Philosophy, but in tracing it through History. In this particular he was in advance of his great compeers in his own department: for he did not hesitate, as Darwin, Spencer, and Huxley did, to deal with the intuitions of his time. Such intuitions as are true being necessarily in advance of knowledge, there is danger of assuming to be true some that are not. This danger kept Huxley almost entirely away from them, and Spencer farther away than any other great philosopher. It was this abstention, certainly excusable and probably justifiable in one who prefers it, that makes his philosophy hated, and prevents its being even studied, not to say understood, by those who love the quagmires and mirages built up by mistaken intuition.