 The next two decades saw no decline in psychologists’ interest in instincts. Between 1900 and 1920 over 600 articles and books were published on this topic in the USA and England alone (Cravens 1978). Many of these publications emulated William James’ work, presenting lists of candidate human and animal instincts. However, these authors often departed from James’ developmental account, viewing instincts instead as emerging fully formed and insensitive to experience. Lists of candidate instincts also varied dramatically, with some authors positing as few as two human instincts and others identifying as many as 110 (L. L. Bernard 1921). William McDougall’s Introduction to Social Psychology (1908) was an attempt to impose rigor to this branch of psychology. McDougall was critical of his fellow instinct theorists, complaining that “[h]undreds of passages might be quoted from contemporary authors, even some of considerable philosophical culture, to illustrate how these two words [‘instinct’ and ‘instinctive’] are used with a minimum of meaning, generally with the effect of disguising from the writer the obscurity and incoherence of his thought” (1908, cited in Herrnstein 1972). McDougall’s solution was to define instincts more precisely as motivational or ‘hormic’ internal states. Specifically, he proposed that instincts are: