فإن القدم ينافي العدم
For eternity is incompatible with nonexistence.
Qidam means beginninglessness. If a given accident is shown to have been absent, or to be subject to nonexistence in the relevant sense, it cannot be beginningless in that same sense.
Two cautions matter:
1. Specify which property's nonexistence is being discussed.
2. The loss of one property by a body does not by itself establish that the whole body originated; an additional premise is needed.
Thus the origination of accidents and the origination of substances occupy distinct stages of the argument.