The drive that produces goal-directed behavior.

The study of motivation is concerned with the influences that govern the initiation, direction, intensity, and persistence of behavior. Three categories of motives have been recognized by many researchers: primary or biological (hunger and the regulation of food intake); stimulus-seeking (internal needs for cognitive, physical, and emotional stimulation, or intrinsic and extrinsic rewards); and learned (motives acquired through reward and punishment, or by observation of others).

Instinct theories, which were popular early in the twentieth century, take a biological approach to motivation. Ethologists study instinctual animal behavior to find patterns that are unlearned, uniform in expression, and...