Mu`tazila (Arabic: المعتزلة‎ al-muʿtazilah) is an school of Islamic theology based on reason and rational thought that flourished in the cities of Basra and Baghdad, both in present-day Iraq, during the 8th–10th centuries. The adherents of the Mu`tazili school are best known for their denying the status of the Qur'an as uncreated and co-eternal with God. From this premise, the Mu`tazili school of Kalam proceeded to posit that the injunctions of God are accessible to rational thought and inquiry: because knowledge is derived from reason, reason is the "final arbiter" in distinguishing right from wrong. It follows, in Mu`tazili reasoning, that "sacred precedent" is not an effective means of determining what is just, as what is obligatory in religion is only obligatory "by virtue of reason."The movement emerged in the Umayyad Era, and reached its height in the Abbasid period. After the 10th century, movement declined and lost any influence it had held. It is viewed as heretical by many scholars in modern mainstream Islamic theology for its tendency to deny the Qur'an being eternal, and to allow for the possibility of free will and thus opposing the strict determinism of mainstream thought. In contemporary jihadism, charges of being a mu`tazili has been used between rivalling group as a means of denouncing their credibility.