Concepts of motion are formed by specifying the distinctive nature of the
motion and of the entities performing it, and/or of the medium in which it is
performed—and omitting the particular measurements of any given instance of
such motion and of the entities involved. For instance, the concept “walking”
denotes a certain kind of motion performed by living entities possessing legs,
and does not apply to the motion of a snake or of an automobile. The concept
“swimming” denotes the motion of any living entity propelling itself through
water, and does not apply to the motion of a boat. The concept “flying” denotes
the motion of any entity propelling itself through the air, whether a bird or
an airplane.