It is my purpose in this section to indicate the relations of my work on monkeys and apes to that of other investigators.  Although throughout the report I have used freely the psychological terms idea and ideation, it has been my aim to describe the behavior of my animals rather than to interpret it or speculate concerning its accompaniments.  Certain acts I have designated as ideational simply because they seemed to exhibit the essential features of what we call ideational behavior in man.  Further study may, and probably will, modify my opinion concerning this matter.  It is of prime importance to analyze ideational behavior so that it may be accurately described and satisfactorily defined in terms of its distinguishing characteristics.  I had hoped to be able to present a tentative analysis in this report, but the results of my efforts are so unsatisfactory that I do not feel justified in publishing them.

The terms idea and ideation have been used to designate contents of consciousness which are primarily representative.  Nowhere have I attempted to indicate different types or grades of ideational behavior and nowhere have I found it necessary to emphasize differences between image and idea.  In general, the acts which I have called ideational have been highly adaptive, and the learning processes in connection with which they have appeared have differed strikingly from those of the selective sort in their abruptness of appearance.

Extremely interesting and valuable definitions of ideation and discussions of the characteristics of different sorts of ideas in the light of original observations on monkeys have been presented by Thorndike (1901, pp. 1, 2; 1911, p. 174); Kinnaman (1902, p. 200); and Hobhouse (1915, p. 270).  As these authors have contributed importantly to our knowledge of the behavior of monkeys, their discussions of the meaning of terms are especially valuable.  Serviceable definitions are to be found, also, in Romanes (1900), Morgan (1906), Washburn (1908), and Holmes (1911).

Evidences of Ideation in Monkeys

Aside from anecdotal and traveller’s notes on the behavior of monkeys and apes we have only a scanty literature.  In fact, the really excellent articles on the behavior and mental life of these animals may be counted on one’s fingers; and not more than half of these are experimental studies.  I shall, in this brief historical sketch, neglect entirely the anecdotal literature, since my own work is primarily experimental, and since its results should naturally be compared with those of other experimenters.

Thorndike (1901), the American pioneer in the application of the experimental method to the study of mind in animals, published the first notable paper on the psychology of monkeys.  His results force the conclusion that “free ideas” seldom appear in the monkey mind and have a relatively small part in behavior.  That the species of Cebus which he observed exhibits various forms of ideation he is willing to admit.  But he insists that it is of surprisingly little importance in comparison with what the general behavior of monkeys as known in captivity and as described by the anecdotal writers have led us to expect.  It is important to note, however, that Thorndike’s observations were limited to Cebus monkeys which, as contrasted with various old world types, are now considered of relatively low intelligence.