Daniel Dennett named three stances one can take towards an object or system. The first is the physical stance in which the physical structure of the system is treated. The second is the intentional stance in which the system is understood in terms of its beliefs, goals and intentions. The third is the design stance in which the system is understood in terms of its composition out of parts. One more stance we'll call the functional stance. We take the functional stance toward an object when we ask what it does without regard to its physics or composition. The example I like to give is a motel alarm clock. The user may not notice whether it is mechanical, an electric motor timed by the power line or electronic timed by a quartz crystal. Each stance is appropriate in certain conditions.