Drive models are at once crude and clever (Hinde 1959). This graphical representation of two hydraulic models of drive shows the crudeness of drive models from physiological and neurobiological standpoints. Their cleverness derives from their attempt to explain, with little knowledge of animals' inner workings, how priorities are decided among competing behaviors.

McFarland and Sibly (1972) suggest analyzing drives as vectors, like vectors of force might be analyzed by physicists. This suggestion has not gained much attention, but it remains the most recent approach to reconciling drive theory with a modern understanding of homeostatic regulation.

Even if drive theory has fallen out of fashion, it holds interesting explanatory value for behavior that results when an animal is either subject to conflicting drives or has "energy" beyond that necessary to achieve the desired consummatory behavior. Two types of behavior are commonly seen as the result of conflicting drives: