All bodies are either in motion or at rest.
AXIOM II.

Every body is moved sometimes more slowly, sometimes more quickly.
LEMMA I.

Bodies are distinguished from one another in respect of motion and rest, quickness and slowness, and not in respect of substance.
Proof .-- The first part of this proposition is, I take it, self--evident.

That bodies are not distinguished in respect of substance, is plain both from I.v.and I.viii.

It is brought out still more clearly from I.xv, note.
LEMMA II.