Ash'arism or Ashʿari theology (//; Arabic: ٱلْأَشْعَرِيَّة al-ʾAšʿarīyah or ٱلْأَشَاعِرَة al-ʾAšāʿirah) is the foremost theological school of Sunni Islam which established an orthodox dogmatic guideline based on clerical authority, founded by the Arab theologian Abu al-Hasan al-Ashʿari (d. 936 / AH 324). The disciples of the school are known as Ashʿarites, and the school is also referred to as the Ashʿarite school, which became the dominant theological school within Sunni Islam. It is considered one of the orthodox schools of theology in Sunni Islam, alongside the Maturidi school and Athari school of theology.
Abu al-Hasan al-Ashʿari was noted for his teachings on atomism, among the earliest Islamic philosophies, and for al-Ashʿari this was the basis for propagating the view that God created every moment in time and every particle of matter. He nonetheless believed in free will, elaborating the thoughts of Dirar ibn 'Amr and Abu Hanifa into a "dual agent" or "acquisition" (iktisab) account of free will.[page needed]
While al-Ashʿari opposed the views of the Mu'tazili school for its over-emphasis on reason, he was also opposed to the view which rejected all debate, held by certain schools such as the Zahiri ("literalist"), Mujassimite ("anthropotheist") and Muhaddithin ("traditionalist") schools for their over-emphasis on taqlid (imitation) in his Istihsan al‑Khaud:
A section of the people (i.e., the Zahirites and others) made capital out of their own ignorance; discussions and rational thinking about matters of faith became a heavy burden for them, and, therefore, they became inclined to blind faith and blind following (taqlid). They condemned those who tried to rationalize the principles of religion as 'innovators.' They considered discussion about motion, rest, body, accident, colour, space, atom, the leaping of atoms, and Attributes of God, to be an innovation and a sin. They said that had such discussions been the right thing, the Prophet and his Companions would have definitely done so; they further pointed out that the Prophet, before his death, discussed and fully explained all those matters which were necessary from the religious point of view, leaving none of them to be discussed by his followers; and since he did not discuss the problems mentioned above, it was evident that to discuss them must be regarded as an innovation.
Ashʿarism became the main school of early Islamic philosophy whereby it was originally based on the foundations laid down by Abu al-Hasan al-Ashʿari who founded the school in the 10th century based on the methodology taught to him by his teacher Abdullah ibn Sa'eed ibn Kullaab. However, the school underwent many changes throughout history resulting in the term Ashʿari, in modern usage, being extremely broad, e.g. differences between Ibn Furak (d. AH 406) and al-Bayhaqi (d. AH 384).
For example, the Asharite view was that comprehension of the unique nature and characteristics of God were beyond human capability. The solution proposed by Abu al-Hasan al-Ashʿari to solve the problems of tashbih and ta'til concedes that the Divine Being possesses in a real sense the attributes and Names mentioned in the Quran. Insofar as these names and attributes have a positive reality, they are distinct from the essence, but nevertheless they do not have either existence or reality apart from it. The inspiration of al-Ashʿari in this matter was on the one hand to distinguish essence and attribute as concepts, and on the other hand to see that the duality between essence and attribute should be situated not on the quantitative but on the qualitative level — something which Mu'tazili thinking had failed to grasp.
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The Ashʿarite view holds that:
Ibn Taymiyyah attacked Ashari thought as (in the words of one historian, Jonathan A.C.Brown) "a Greek solution to Greek problems" that should "never" have concerned Muslims. Both Shah Wali Allah and Ibn Taymiyyah rejected the lack of literalism in Ashʿari “speculative theology” and advocated "straightforward acceptance of God’s description of Himself.”
On the other hand, German orientalist Eduard Sachau blamed the theology of Ashʿari and its biggest defender, al-Ghazali, specifically for the decline of Islamic science starting in the tenth century, and stated that the two clerics were the only obstacle to the Muslim world becoming a nation of "Galileos, Keplers and Newtons." However Joseph E. B. Lumbard offered a refutation claiming that there is no historical evidence to substantiate such a claim, and in fact science continued to prosper. He states that this myth originates from a poor reading of Ghazali warning against the abuse of new technology and how it can disrupt and harm society if not properly implemented. Similar to how nuclear weapons, artificial intelligence and stem cell research today is restricted to a degree for ethical reasons. 
Many others also agree and argue that the Ashʿarites not only accepted scientific methods but even promoted them. Ziauddin Sardar points out that some of the greatest Muslim scientists, such as Ibn al-Haytham and Abū Rayhān al-Bīrūnī, who were pioneers of the scientific method, were themselves followers of the Ashʿari school of Islamic theology. Like other Ashʿarites who believed that faith or taqlid should apply only to Islam and not to any ancient Hellenistic authorities, Ibn al-Haytham's view that taqlid should apply only to prophets of Islam and not to any other authorities formed the basis for much of his scientific skepticism and criticism against Ptolemy and other ancient authorities in his Doubts Concerning Ptolemy and Book of Optics.
Some authors have questioned the spiritual value of discussion methods employed by the Ashʿarites and other dialectical theologians. Fakhr al-Din al-Razi, himself a leading figure of the Ashʿari school, said at the end of his life: "I employed all the methods which philosophy and dialectic had provided, but in the end I realised that these methods neither could bring solace to the weary heart nor quench the thirst of the thirsty. The best method and the nearest one to reality was the method provided by the Qur'an."[self-published source]