Most of the philosophy of the physician whom Latin Europe called Rhazes survives only in the books of men who wrote to refute him. Abū Bakr Muḥammad ibn Zakariyyāʾ al-Rāzī made his name in medicine. His biographers report that he ran a hospital in his home city of Rayy, near modern Tehran, and another in Baghdad. For his patron Abū Ṣāliḥ al-Manṣūr, the governor of Rayy, he wrote a medical handbook, the Kitāb al-Manṣūrī. In The Philosophical Way of Life he counts nearly two hundred books, treatises and letters of his own. Of his philosophical works, only two survive complete, and both are about how to live.
What runs through all of it is a confidence in reason. God, as al-Razi saw it, gives reason (ʿaql) equally to every human being, and reason alone is enough to judge any authority, however great. He treated Galen, the Greek physician of the second century, as the greatest of medical authorities, and still wrote a whole book, the Doubts about Galen, listing where Galen was wrong — on the grounds that Galen himself had criticised his own predecessors. When Galen argued that the world must be eternal because it never seems to change, al-Razi answered that a building can stand unchanged for ages and then collapse all at once.
His picture of the world reaches us through hostile reporters, chief among them two Ismaili writers: Abū Ḥātim al-Rāzī and Nāṣir-i Khusraw, a Persian of the eleventh century. (The Ismailis, a branch of Shia Islam, hold that the faithful need an imam, a religious leader, to guide them to the true understanding of Islam.) In their accounts, five things have always existed: God, Soul, matter, time and place. The world is well designed, yet full of suffering, so God cannot have made it directly. Soul, foolish where God is wise, desired to mix with matter; God then shaped the result as well as it could be shaped, and gave Soul reason so that it could learn to free itself. Matter itself, on this view, is made of atoms and empty space. To Abū Ḥātim and Nāṣir-i Khusraw, four eternal principles beside God were a grave departure from Islam.
His views on prophecy caused the greater scandal. Abū Ḥātim describes face-to-face debates in which al-Razi argued that it would be unjust for God to give useful knowledge to a chosen few, that leaders appointed by revelation only breed quarrels among their followers, and that believers who accept doctrine on authority alone fail to use the reason God gave them. His books on prophecy are lost, and scholars disagree about what they said. Some read him as a freethinker who rejected every revelation. Others point to Fakhr al-Dīn al-Rāzī, a theologian from the same city who wrote centuries later: he reports al-Razi interpreting the Qurʾān as agreeing with his own philosophy. Some suggest that al-Razi's real target was the Ismaili doctrine of the imam.
The two ethical works let him speak for himself. The Spiritual Physick (al-Ṭibb al-rūḥānī), written for the same governor al-Manṣūr, treats envy, anger and the fear of death the way his handbook treats the body's diseases. The Philosophical Way of Life (al-Sīra al-falsafiyya) answers critics who called him a hypocrite: he claimed Socrates as his model, yet lived among people and earned a living. Socrates, he replied, gave up his early severity as he grew older; the philosopher's task is to imitate God as far as a human being can, through knowledge, justice and mercy, and that mercy extends to animals. In the same pages he mentions that years of reading and copying had damaged his eyes and a hand. A third treatise, on nature and motion, was printed among his writings, though some scholars doubt that he wrote it. All three are held here, in Arabic.
Ismaili writers kept attacking him; Maimonides, the Jewish philosopher, attacked his explanation of suffering in the Guide of the Perplexed; and Avicenna judged that he had overreached in medicine and philosophy alike. Few later philosophers took up his ideas, but the physician fared better. Under the name Rhazes his medical books went through sixty-seven printed editions in Europe before 1700. Reference works disagree on his dates: the Stanford Encyclopedia of Philosophy gives 865 to 925, while Britannica gives about 854 for his birth and 925 or 935 for his death. His surviving philosophical writings were collected by the Arabist Paul Kraus and printed in Cairo in 1939.