Bahshamiyya (, also known as "Ba Hashimiyya") was a Mu'tazili-influenced school of thought, rivaling the school of Abd al-Jabbar ibn Ahmad, based primarily on the earlier teaching of Abu Hashim al-Jubba'i, the son of Abu 'Ali Muhammad al-Jubba'i.
Borne from Mu'tazila
Mu'tazila is a school of rationalist Islamic theology known as Kalam. Early practitioners stressed the supremacy of human reason and free-will (similar to Qadariyya) and went on to develop an epistemology, ontology and psychology which provide a basis for explaining the nature of the world, God, man and religion. According to Mu'tazilis, good and evil are easily reconciled through human reason without esoteric methods.
The Mu'tazila school started in the 8th century; its iterative refinement continued from the late 10th century until mid-11th century CE. Mu'tazila was briefly the official theology of the Abbasid caliphs in the 9th century. The impact of Mu'tazila doctrine continues to be felt in primarily three groups: Shi'a (Ismai'li) Islam, Karaite Judaism, and to a much lesser extent Rabbanite Judaism of the Sephardic Rite and Yemenite rite.
Two Schools
By the end of the 9th century Mu'tazila had split into two schools:
1. the Baghdad school Ikhshīdiyya - followed modifications by Abu Yaqub Yusuf al-Shahham, who adopted the idea of "acquisition" (kasb, iktisab), applied it only to involuntary human actions, God-being, in their view, in no way the "cause" of free human actions; for al-Jubbai, on the contrary, God retains Supreme Power even over the actions which man performs freely. But, unlike the later Ashari notion, Al-Jubba'i refuses to apply the theory of the kasb to free actions; and he calls man the "creator" (Khalik) of his actions, in the sense that man acts, or his actions proceed from him, with a determination (Qadar) which comes from God. Al-Jubbai had two pupils who later became celebrated 1) his son Abu Hashim and 2) Abu'l-Hasan al-Ash'ari who, after breaking away, was to devote himself to refuting Mu'tazila and to become the "founder" of the so-called school of the Ashariyya. The traditions of the ilm al-kalam take pleasure in recounting the dialogue reputed to have brought Al-Ashari and his teacher into conflict on the subject of the fate of the "three brothers"-one pious, one impious and one who died infans. In this issue was posed the problem of the rational justification of the divine Decree. Al-Jubbai was unable to reply with a coherent answer and al-Ashari left him to start his own school.
2. the Basra School Bahshamiyya - see below
Bahshamiyya ascendance
The Basra school was led by Abū 'Alī al-Jubbā'ī and his son Abū Hāshim. Students and followers of Abû Hâshim formed a sub-school known as the Bahshamiyya. The most noteworthy practitioners were:
1. Abū 'Alī ibn Khallād
2. Abū 'Abd Allāh al-Basrī
3. Abū Ishāq ibn 'Ayyāsh
Abd al-Jabbār al-Hamadānī, a judge, was a student of Abû 'Abd Allâh and Abû Ishâq and a very prolific author of Mu'tazili doctrine. One of Abd al-Jabbâr's own students, Abu'l Husayn al-Basrī, was once thought to establish the last creative school of thought among the Mu'tazila - Husayniyya Mu'tazila.
Bahshamiyya Mu'tazila and Judaism
In Judaism (Rabbanite and Karaite) Bahshamiyya Mu'tazila was adopted in Sura and Pumbeditha Academies of Babylon, in varying degrees, from the 9th century onwards. Jewish Gaonim composed works which reflected Mu'tazila influence as well as translated many of the Arabic Mu'tazila texts into Hebrew (i.e. Yûsuf al-Basîr's al-Kitâb al-Muhtawî and Kitâb al-Tamyîz). The influence of Bahshamiyya Mu'tazila quickly became central to Jewish religious and intellectual life in the East - slowly migrating across North Africa with the Fatmimids and making it way to al-Andalus. Gaonim who embraced Bahshamiyya Mu'tazila included Samuel ben Hofni Gaon who was familiar with the works of Ibn Khallâd and Abû 'Abd Allâh al-Basrî as well as Saadiah Gaon.
Mu'tazilî doctrines and terminology provided a basis for discussion and polemical exchanges between Jewish and Shi'a scholars. Virtually banned from Sunnî Islam, Mu'tazila doctrine remains an integral part of Islamic intellectual history. The rationalistic approach of Mu'tazila towards reasoned theological issues led to the classification of Mu'tazilîs as freethinkers within Islam who had been deeply influenced by Greek philosophical thought and thus practiced apostasy and heresy. A similar attitude was assumed by Tosafists and Kabbalists towards "Jewish Kalam"