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.