We have perfectly good evidence of the law of "unitary response to multiple stimuli" from the physiological study of reflex action; and we have perfectly good anatomical evidence of the convergence and divergence of neural paths of connection, as required by the law of combination. The association fibers extending from one part to another of the cortex are an anatomical fact. [Footnote: See p. 56.] Facilitation is a fact, and that means that a stimulus which could not of itself arouse a response can coöperate with another stimulus that has a direct connection with that response, and reinforce its effect. In short, all the elements required for a neural law of combination are known facts, and the only matter of doubt is whether we have built these elements together aright in our interpretation. It is not pure speculation, by any means. {418} EXERCISES 1. Outline the chapter, in the form of a list of laws and sub-laws. 2. Review the instances of learning cited in Chapters XIII-XV, and examine whether they are covered and sufficiently accounted for by the general laws given in the present chapter. 3. Draw diagrams, like those given in this chapter, for the simpler cases, at least, that you have considered in question 2. 4. Show that response by analogy is important in the development of language. Consider metaphor, for example, and slang, and the using of an old word in a new sense (as in the case of 'rail-road'). REFERENCES William James devoted much thought to the problem of the mechanism of learning, habit, association, etc., and his conclusions are set forth in several passages in his _Principles of Psychology_, 1890, Vol. I, pp. 104-112, 554-594, and Vol. II, pp. 578-592. Another serious consideration of the matter is given by William McDougall in his _Physiological Psychology_, 1905, Chapters VII and VIII. See also Thorndike's _Educational Psychology, Briefer Course_, 1914, Chapter VI. On the whole subject of association, see Howard C. Warren, _A History of the Association Psychology_, 1921. {419} CHAPTER XVII PERCEPTION MENTAL LIFE CONSISTS LARGELY IN THE DISCOVERY OF FACTS NEW TO THE INDIVIDUAL, AND IN THE RE-DISCOVERY OF FACTS PREVIOUSLY OBSERVED