Reinforcers comprise sequences of actions in context. Just as the white of snow and black of coal depend on the interaction of an organism's visual system and the reflectances in its surrounds, reinforcers depend on an organism's motivational state and the affordances-possibilities for perception and action-in its surrounds. Reinforcers are not intrinsic to things but are a relation between what the thing affords, its context, the organism, and his or her history as capitulated in their current state. Reinforcers and other affordances are potentialities rather than intrinsic features. Realizing those potentialities requires motivational operations and stimulus contexts that change the state of the organism-they change its disposition to make the desired response. An expansion of the three-term contingency is suggested in order to help keep us mindful of the importance of behavioral systems, states, emotions, and dispositions in our research programs.