who refrain from either denying or affirming its existence. If the existence of an indivisible atom is not known, this argument is invalid. Moreover, even if the indivisible atom exists, it is undoubtedly imperceptible to the senses, so one cannot know through sense perception whether a substance is like it or unlike it. Consequently, one cannot know that substances are all alike. Rather, it may be said that they are not alike, just as has been said of bodies.

We have already discussed the disagreement over whether substances constitute one genus, two, three, five, or more. Even those who say they constitute a single genus do not say that they are all alike, just as, in their view, animal is a genus, yet its members are not all alike.

His statement: “In that case, it is not inconceivable to reason that there exist substances whose occupancy of their particular spatial regions is necessary. Thus, the proof that bodies have a temporal beginning would not apply to those things.”

The reply is: There is no doubt that you have based your approach to proving that the world has a temporal beginning on this principle. Yet anyone who considers the proofs he presents on this and similar questions will see that what he presents on