Mutazila

Mutazili theology organised itself around five principles, and the school treated holding all five, rather than any one of them, as what made a person a Mutazili.

The first is tawhid, the divine unity, taken in a strict sense. The attributes of God are not entities standing alongside the essence, because that would make eternal things other than God himself. God knows by his essence rather than by a knowledge distinct from it, and the Quran, being speech, is something God does rather than something God eternally is, and is therefore created.

The second is adl, justice, and it does the heaviest work in the system. God cannot do wrong, not because some external rule forbids it but because wrongdoing is incompatible with what God is. Good and evil are accordingly real properties that human reason can recognise without waiting for revelation, and God will not act against them. From this the school derived human free agency, because a person must genuinely originate their own acts or the reckoning at the judgement would punish someone for what God had done.

The third and fourth are the promise and the threat, meaning that God will certainly carry out both and cannot simply waive the second, and the intermediate position, which places a Muslim who commits a grave sin in a category between belief and unbelief rather than forcing the choice between them.

The fifth is commanding right and forbidding wrong, understood as a duty on the community which could in principle extend to acting against an unjust ruler.

The fortunes of the school turned on a caliph. Al-Mamun adopted the doctrine of the created Quran and in 833 imposed it as a test on judges and scholars, an episode known as the mihna. His two successors continued it and al-Mutawakkil abandoned it around 848. That reversal is why Mutazilism is remembered in Sunni Islam as a defeated position, and it handed its opponents a durable argument as well, since a theology that had reached for the machinery of the state to settle a question could afterwards be presented as having lost the argument on its merits.

What followed was not disappearance. Mutazili positions were adopted almost entire by Zaydi Shia theology in Yemen and substantially by Twelver Shia theology, where the insistence on divine justice and on reason having access to moral truth is still standard. The Ashari and Maturidi schools that displaced the Mutazila in Sunni Islam were built specifically to answer them, and they kept the vocabulary and much of the method of argument even where they rejected the conclusions.

Most of what is known about the school from its own side, rather than through the reports of the people who refuted it, comes from manuscripts preserved in Zaydi libraries in Yemen. The recovery in the twentieth century of the greater part of the Mughni of Abd al-Jabbar, a systematic work running to many volumes, changed the field considerably, because until then a school that had argued for the sufficiency of reason was being read almost entirely through summaries written by its opponents.