The Progression to Infinity

It is evident therefore that everything which is moved is moved by something. It is necessary therefore if anything ceases to be moved because something else stands still that this thing should be moved by something else. This however does not proceed to infinity, but it stops somewhere and there will be something which will be primarily the cause of motion. Let A be moved by B, B by C and C by D and after this manner let there be a progression to infinity.