The older psychologists were not acquainted with the as yet undiscovered truths of evolution, and studied mind without their aid. Practically they dealt only with the fully developed thing as manifested in man. From that point of view, by "introspection," by observation of their own conscious states, they sought information regarding their own minds, and by "legitimate inferences" information regarding the minds of other men, and to a much less extent, information regarding the minds of lower animals. "Introspection" and "legitimate inferences" are still our only sources of information, but the "legitimate inference" that there is kinship between the human and the brute intellect, and that in the brute we may see the beginnings of that which we observe in man, enables us to make a better use of our available information. By observing mind at its beginning, and tracing it during its evolution, we are enabled to an extent undreamed of by former generations to understand of what it is compounded, to analyze it.
To Mr. Herbert Spencer beyond all others is due the credit of having applied the doctrine of evolution to the study of psychology, with the result that this science,