It is far from my intention to say that inheritance is not as specific nervously as it is in matters of blood pressure and texture of skin. As we, in our limited knowledge, still define abilities in terms of behaviour and not by nervous elements, my contention is that intelligence should be regarded as the sum total of this inheritance, much as general strength is, in terms of the body. We have still to find the component units of this intelligence. We can then define predisposition to ability. To split intelligence into inherited units of mathematics, reading, composition, mechanics, etc., is as unjustifiable as to split inherited vigor of body into baseball capacity, running capacity, climbing capacity, etc. Mathematics and music are what we do with intelligence, not what intelligence is made of. Of course everyone agrees to this. The lack of emphasis upon the chance that the inherited units are general in their application, that the same inherited elements are involved in many of the behavior complexes which we call traits and abilities, is what confuses the situation. CURRENT PSYCHOLOGICAL OPINION We must know what these elements are, and how many contribute to which capacities. Then we can decide the question of specialized inheritance. In all crude behavior data it is impossible to separate the influence of nature and nurture. A theory of specialized inheritance will inevitably infringe upon common sense in its claims. Of the following statements, it would be easier for most of us to endorse 1 and 2 than 3 and 4, whereas few would agree with 5 and 6. 1. “Unless one is a blind devotee to the irrepressibility and unmodifiability of original nature, one cannot be contented with the hypothesis that a boy’s conscientiousness or self-consciousness is absolutely uninfluenced by the family training given to him. Of intelligence in the sense of ability to get knowledge rather than amount of knowledge got, this might be maintained. But to prove that conscientiousness is irrespective of training is to prove too much.” (Thorndike, _Educational Psychology_, III, pp. 242.) 2. “Some attempts have been made to apply these laws to behavior complexes, but as yet psychology has provided little foundation for such studies. The most thorough-going attempts have been made with human mental traits and some evidence has been collected here in favor of the view that differences in the instinctive behavior of individuals are inherited according to Mendelian ratios. _But in the field of human psychology too little is known of the genesis of character, of the distinction between nature and acquired behaviour to provide a very firm foundation for the work of the geneticist._” (Watson, _Behaviour_, p. 156. Italics are mine.)