_Evolution as a Method of Study._ In a third sense the word evolution is applied to a method of investigation. It is the study of present conditions in the light of the past. The preliminary work of science is the descriptive part. This involves accuracy of observation and precision of statement, but makes no great demands on the powers of logical analysis and synthesis. The easy work of science is largely already done. Those who would continue investigation must study not only facts and structures, but the laws that govern them. In the words of John Fiske, "Whether plants or mountains or mollusks or subjunctive moods or tribal confederacies be the things studied, the scholars who have studied them most fruitfully were those who have studied them as phases of development. Their work has directed the current of thought." The most difficult problems in life are susceptible of more or less perfect solution if approached by the method of evolution. They cannot be even stated as problems in any other terms. In every science worthy of the name the history of origins and the study of developing forces must take a leading part. _Evolution as a System of Cosmic Philosophy._ In a fourth sense the word evolution has been applied to the philosophical conceptions to which the theory of evolution gives rise. Philosophy is not truth. When it is so it becomes science. At the best it points the way to truth. The broader the inductive basis of any system of philosophy, the greater its value as an intellectual help. The system of Herbert Spencer, the greatest exponent of the philosophy of evolution, is based wholly on the results of scientific investigation. It consists of a series of more or less broad and more or less probable deductions from the facts and laws already known. Systems like these, which rest on scientific knowledge, do not rise high above it. They can therefore be revised or rewritten as knowledge increases. They provide the means for their own correction. Systems resting on aphorisms or assumptions or definitions must disappear as knowledge increases. Philosophy is never wholly identical with truth. The partial truth which it may contain becomes wholly error with the advance of science. The growth of exact knowledge transforms the truth in philosophy into science, leaving the absolute falsehood as the final residuum.