They disagree over matters addressed by the revealed texts, such as the divine attributes and divine decree. As for newly devised questions—such as the indivisible atom, whether bodies are alike, the persistence of accidents, and other matters—their disputes are too extensive to recount fully, yet each claims rational certainty concerning them.
Moreover, the further people depart from the sunnah, the greater their disputes and disagreements concerning what they regard as rational knowledge. Thus, the Muʿtazila disagree more extensively than the speculative theologians who affirm the divine attributes. The disputes between their Basran and Baghdadi schools would take a long time to recount. The Basrans are closer to the sunnah and to affirming the divine attributes than the Baghdadīs. Hence, the Basrans affirm that the Creator is All-Hearing and All-Seeing, as well as Ever-Living, All-Knowing, and All-Powerful, and they affirm His will. They do not hold that doing what is most beneficial in worldly affairs is obligatory; they accept solitary reports and analogical reasoning; and they do not deem scholars who exercise independent judgment sinful, among other positions.
Then there are the well-known disputes between the Mashāyikha and the Husayniyya—the followers of Abū al-Hasan al-Basrī.
As for the Shia, they are even more divided and contentious than the Muʿtazila, because they are further removed from the sunnah. Indeed, it has been said that they number seventy-two sects.
As for the philosophers, no common principle unites them. Rather, their disagreements are greater than those of all the Muslim, Jewish, and Christian groups.
The philosophy adopted by al-Fārābī and Ibn Sīnā is simply that of the Peripatetics, the followers of Aristotle, author of the philosophical teachings. The disputes and disagreements between him and his predecessors would take a long time to describe, as would the disagreements among his followers.
As for the other schools of philosophers, merely recounting their disagreements in astronomy would reveal more disagreement than exists within any single group of those who face the qiblah. Astronomy is a mathematical science based on calculation, which is