In his monumental Book of Doctrines, when Abū al-Ḥasan al-Ashʿarī set forth the creeds of non-Muslims—and in the same way Abū ʿĪsā al-Warrāq, Qāḍī Abū Bakr ibn al-Ṭayyib, and others who collect people’s opinions and debate them— they reported so many divergent statements of the philosophers that the words of the Peripatetics amount to little amid a vast multitude.

Now, if the ultimate aim of their philosophy is nothing more than knowledge of abstract universals that possess no existence outside the mind—while what exists externally are only concrete particulars—then there is nothing in the external world that corresponds to the soul such that the soul could be perfected and made happy by knowing it. It therefore becomes clear that what they have asserted about the soul’s perfection and felicity after death is error and misguidance.

Eleventh Point
Universals correspond to their particulars. When the particulars are liable to change from one state to another, the universals cannot remain constant; thus knowledge of them is not knowledge of anything enduring. Every created being, as the Messengers have informed us and sound reason affirms, is subject to transformation. If, then, there are no eternal, everlasting intelligible universals within existing things that are immune to change, whatever universals connected to created entities reside in the soul amount to ignorance, not knowledge.

Consider, for example, the natural universal, “fire burns.” Burning is contingent upon certain conditions and hindered by certain impediments: fire may fail to burn because a condition is missing or an obstacle is present, and those obstacles are not confined to any determinate limit. Hence one can never possess decisive knowledge that every fire actually burns what it normally burns. Yet these philosophers still claim that the celestial spheres are pre-eternal and everlasting—and the same, they say, applies to the intellects and the souls.