Motive, spring, impulse, incentive, inducement, spur, goad all denote a stimulus inciting or prompting a person to act or behave in a definite way.
Motive applies chiefly to such an emotion as fear, anger, hatred, or love or to a desire (as for fame, wealth, knowledge, supremacy, or revenge) or to such a physical appetite as hunger or sexual desire which operates on the will and definitely moves it to activity.
Spring, often as the plural springs, is used in place of motive without much difference in meaning; however, it may refer to the underlying or basic motive which is often not fully recognized even by the person affected and is especially hidden from all but the most penetrating observers.
Impulse need not imply, as motive and spring regularly imply, actual performance of an act or engagement in an activity; the term stresses impetus, or driving power, rather than its effect; thus, one may check, or restrain, or forgo, or dismiss an impulse. In its more general sense impulse is applicable to a powerful incitement or instigation to activity, especially one arising within oneself as the result of a native propensity, one's peculiarity of temperament, or one's intellectual or emotional constitution.
Specifically, impulse is applicable to a spontaneous and often unconsidered and nearly irresistible urge to do something.
Incentive applies chiefly to a cause which incites and encourages action or activity and especially to one for which the person affected is not himself responsible or which does not originate within himself.
Inducement is narrower than incentive, for it consistently suggests an external influence and often an attempt to entice or allure to action or activity.
Spur applies to an impetus to action which not only incites but stimulates the mind and increases its energy and ardor.
Goad applies to a stimulus to action or activity that keeps one going in spite of one's will or desire.