Why do they not accept accidental motion for fixed substances as valid?

Why do they not accept accidental motion for fixed substances as valid? The answer is that substantial motion is the very existence of the substance, and is merely in need of a divine generative agent, and the granting of existence to the substance is the same as the granting of existence to the substantial motion. However, the granting of existence to the substance is not the same as the granting of existence to accidents and to motion in accidents.

For this reason, the motion in accidents is related to substantial nature, and is considered an action for it. Such an action is in need of a natural agent whose transformation shows a transformation in its agent. Another very precise objection can also be raised against this argument, the…