two sources, each of which precedes what is generated from them. Once this is clear concerning sunlight, it is also clear concerning the rays of a lamp and other luminous objects, since fire has rays just as the sun does. These, then, are the examples they draw from visible things.

As for their examples drawn from audible things, they cite sounds arising from movements, as in the ringing produced by a tap. The response is that the same applies here: sound is not generated by a single thing. Rather, two things are required—two bodies, one of which strikes the other or separates from it. These are two sources of the sound generated from them, just like the two sources of the rays. These two sources—the two moving bodies—precede the sound in time.

If it is said, “What is meant by the cause is the motion that generates the sound and the positioning of one body opposite another that generates the rays,” the response is: motion and sound, and opposite positioning and rays, may be simultaneous. If they are simultaneous in time, neither precedes the other in any respect. On this assumption, we do not concede that motion and opposite positioning are the causes of sound and rays. Rather, the cause is the agent that produces the motion and the agent that brings about the opposite positioning. And if