If we present to reason that which comes into being, without considering either its individual instances or its kind, and ask, “Must it be bounded and discontinuous, with a beginning, or can it continue perpetually?” we find nothing in reason that requires the kind of things that come into being to be bounded and to have a beginning.

Anyone who reflects on this subject will recognize the distinction between an infinite regress of efficient causes—which is impossible—and an endless succession of effects, one effect after another, as explained at length elsewhere.

The point here is to distinguish between a member of the Zanj and something that comes into being. To clarify this: if we say, “Every member of the Zanj is black,” there can be no member of the Zanj who is not black, because this negation contradicts that affirmation. Of two contradictory propositions that cannot both be false, the truth of one necessarily entails the falsity of the other. Thus, saying, “Some members of the Zanj are not black,” contradicts saying, “Every member of the Zanj is black.” If none of the Zanj is not black, it necessarily follows that they are all black.

But if we say, “Everything that comes into being has a beginning,” it follows that nothing among the things that come into being lacks a beginning; and likewise for its contrapositive,