Full Idea
It is the nature of light and heavy things to tend in certain directions, and this is what it is to be light or heavy; to be light is defined by an upwards tendency, and to be heavy is defined by a downwards tendency.
Gist of Idea
Heavy and light are defined by their tendency to move down or up
Source
Aristotle (Physics [c.337 BCE], 255b14)
Book Reference
Aristotle: 'Physics', ed/tr. Waterfield,Robin [OUP 1996], p.199
A Reaction
The discredited 'teleological' view of gravity, and yet if we define 'heavy' in Newtonian terms we are in danger of circularity, and of proposing laws which are bafflingly imposed from outside. Hence the 'New Essentialists' prefer Aristotle's view.