Ibn Rushd said:

“As for the Mu'tazilites, none of their books has reached us in this peninsula from which we might learn the methods they followed in this matter. Their methods would seem to be of the same kind as those of the Ash'arites.”

I say:

The Mu'tazilites’ method is the very method he attributed to the Ash'arites; those who adopted it merely borrowed it from them. Thus, since al-Ash'arī sometimes agreed with them and sometimes with the early generations, the imams, and the adherents of hadith and the Sunnah, he condemned this method, as his previously quoted words show. In condemning and criticizing it, he agreed with the early generations and the imams.

Ibn Rushd read such Ash'arite books as were available to him and saw their reliance on this method. That is why he discussed it.

The most outstanding of the later Mu'tazilites was Abū al-Husayn al-Basrī. He relied on this method in all his books, even the one he entitled Ghurar al-adilla (The Choicest Proofs).