In this article, I argue that affordances are properties of the animal-environment system, that is, that they are emergent properties that do not inhere in either the environment or the animal. I critique and review the formal definition of affordance offered by Turvey (1992). Turvey defined affordances as properties of the environment; I discuss some consequences of this and argue that Turvey's strategy of grounding the definition of affordance in terms of dispositional properties is problematic. I also suggest that Turvey's definition of affordance may lead to problems for the specification and direct perception of affordances. Motivated by these problems, I propose a new definition of affordance, in which affordances are properties of the animal-environment system. This definition does not rely on the concept of dispositional properties and is consistent with direct perception.