The equipment of instincts with which a human being is at birth endowed must be considered in two ways. It consists, in the first place, of definite and unlearned mechanisms of behavior, fixed original responses to given stimuli. These are, at the same time, the original driving forces of action. An instinct is at once an unlearned mechanism for making a response and an unlearned tendency to make it. That is, given certain situations, human beings do not simply utilize inborn reactions, but exhibit inborn drives or desires to make those reactions. There is thus an identity in man's native endowment between what he can do and what he wants to do. Instincts must thus be regarded as both native capacities and native desires. Instincts define, therefore, not only what men can do, but what they want to do. They are at once the primary instruments and the primary provocatives to action. As we shall presently see in some detail, human beings may acquire mechanisms of behavior with which they are not at birth endowed. These acquired mechanisms of response are called habits. And with the acquisition of new responses, new motives or tendencies to action are established. Having learned how to do a certain thing, individuals at the same time learn to want to do it. But just as all acquired mechanisms of behavior are modifications of some original instinctive response, so all desires, interests, and ideals are derivatives of such original impulses as fear, curiosity, self-assertion, and sex. All human motives can be traced back to these primary inborn impulses to make these primary inborn responses.[1] [Footnote 1: The clearest statement of the status of instincts as both mechanisms of action and "drives" to action has been made by Professor Woodworth in his _Dynamic Psychology_. No one else, to the best of the author's knowledge, has made the distinction with the same clarity and emphasis, though it has been suggested in the work of Thorndike and McDougall. In McDougall's definition of an instinct he recognizes both the responsive self and the tendency to make the response. An instinct is, for him, an inherited disposition which determines its possessor, in respect to any object, "to act in regard to it in a particular manner, or at least to experience an impulse to such action."]