ABSTRACT
The first Cartesian law is that every body, 'quantum in se est', remains in the same state, whether of motion or rest, until some external cause impedes or propels it. The second law is that, of itself, movement is in straight lines. The third law concerns impact, which Descartes saw in terms of a conflict of forces, a force to move and a force to resist motion, the latter being a distinct force of rest. In general the 'stronger' body transfers some of its motion to the 'weaker'. The rules for the application of this law to specific cases distinguish the opposition between movement and rest in the two bodies from the opposition between the determination of one body to move in a given direction and the power of the other body to alter that direction according to the direction of its own movement.
