First:
He and his predecessors erred in thinking that, outside the mind, there exists a real entity that can accommodate both alternatives and is simultaneously qualified by existence and non-existence—just like those who say, “The non-existent is a thing.” I have dealt with this at length elsewhere and shown that the correct view is that the notion conceived by the intellect is the one to which the judgment applies: it may come to exist in the external world, or it may remain nonexistent. In the same way, when we declare something impossible—such as the conjunction of two contradictories—what we mean is that the very concept envisaged by the mind cannot possibly obtain in concreto.

Second:
He and those who follow him departed from their own predecessors by imagining that the eternal, pre-existent, Necessary Being could, in relation to something else, be merely possible and therefore susceptible to non-existence. In doing so they combined two opposites: affirming that it is impossible for Him to cease to be, yet also claiming that He can accept non-existence. The only way to speak of His accepting non-existence is to envisage His essence stripped of the necessitating factor—an assumption that is itself impossible. Hence He would admit non-existence only on the basis of an impossible hypothesis, and whatever rests on an impossible hypothesis is itself impossible. They have thus brought two contradictories together, and this has given rise to objections for which they have no answer, as has been set out in various places, such as the critique of al-Muḥaṣṣal and others.

Our purpose here is to complete his argument that all originated things need a perpetual cause, so that, by the very proof they deem rationally sound, it becomes plain that everything apart from God is originated.

He said: “It follows from this that the effects stand in need, for their very explanation…"