`Amr b. Bahr al-Jahiz (d. 255), the third of an-Nazzam’s pupils mentioned above, may be regarded as the last of the middle period of the Mu`tazilites. He was an encyclopædic writer according to the fashion of the time and wrote on literature, theology, logic, philosophy, geography, natural history, and other subjects (cf. Masudi viii. 33, etc.) To free will he gives rather a new bearing. The will he regards as simply a manner of knowing and so as an accident of knowledge; a voluntary act he defines as one known to its agent. Those who are condemned to the fire of hell do not suffer eternally by it, but are changed by its purification. The term “Muslim” must be taken to include all who believe that God has neither form or body, since the attribution of a human form to God is the essential mark of the idolater, that he is just and wills no evil, and that Muhammad is his prophet. Substance he treats as eternal, accidents are created and variable.
We have now reached the third stage of the history of the Mu`tazilites, that which marks their decline. During this latter period they divide into two schools, that of Basra giving its attention mainly to the attributes of God, that of Baghdad being chiefly occupied with the more purely philosophical discussion of what is meant by an existing thing.
The Basrite discussions received their final form in the dispute between al-Jubbay (d. 303) and his son Abu Hashim (d. 321). The latter held that the attributes of God are distinct modes of being, we know the essence under such varying modes or conditions, but they are not states, nor are they thinkable apart from the essence, though they are distinct from it but do not exist apart from it. Against this his father objected that these subjective attributes are only names and convey no concept. The attributes are thus asserted to be neither qualities nor states so as to imply subject or agent, but they are inseparably united with the essence.
Against all views of this sort the orthodox adhered, and still adhere to the opinion that God has real qualities. Those who laid emphasis on this in opposition to the Mu`tazilite speculations are commonly known as Sifatites (sifat, qualities), but they admit that, as God is not like a man, the qualities attributed to him in the Qur´an are not the same as those qualities bearing the same names which are referred to men, and it is not possible for us to know the real import of the qualities attributed to God.
A more pronounced recoil against the Mu`tazilite speculations appears in Abu `Abdullah b. Karram (d. 256) and his followers who were known as Karramites. These returned to a crude anthropomorphism and held that God not only has qualities of precisely the same kind as a man may have, but that he actually sits on a throne, etc., taking in plain literal sense all the statements made in the Qur´an.
The Mu`tazilite school of Baghdad concerned itself mainly with the metaphysical question—“what is a thing?” It was admitted that “thing” denotes a concept which could be known and could serve as subject to a predicate. It does not necessarily exist, for existence is a quality added to the essence: with this addition the essence becomes an entity (mawjud), without this addition it is a non-entity (ma`dum) but still has substance and accident, so that God creates by adding the single attribute of existence.
The whole course of Mu`tazilite speculation shows the influence of Greek philosophy as applied to Muslim theology, but the influence is for the most part indirect. The ideas of Aristotle, as the course of speculation projected to the forefront the problems with which he had dealt in times past, were received through a Syriac Christian medium, for the most part imperfectly understood and somewhat modified by the emphasis which Christian controversy had given to certain particular aspects. More or less directly prompted by the Mu`tazilite controversy we have three other lines of development: in the first place we have the “philosophers” as the name is used by the Arabic writers, meaning those students and commentators who based their work directly on the Greek text or at least on the later and better versions. In their hands philosophical enquiry took a somewhat changed direction as they began to understand better the real meaning of what Aristotle had taught. In the second place we have the orthodox theology of al-Ash`ari, al-Ghazali, and others, which represents Muslim theological science as modified and partly directed by Aristotelian philosophy, consciously endeavouring to make a working compromise between that philosophy and Muslim theology. The older Mu`tazilite tradition came to an end in the time of al-Ash`ari: men who felt the force of philosophical questions either adopted the orthodox scholasticism of al-Ash`ari and those who came after him, or followed the course of the philosophers and drift away from the traditional beliefs of Islam altogether. In the third place we have the Sufi movement, in which we find neo-Platonic elements mingled with others from the east, from India and Persia. The Mu`tazilites proper come to an end with the fourth century A.H.