His chief medical work was known as the _Kulliyat_, “the universal,” which, under the Latinized name of “colliget,” became popular as a manual in the mediæval universities where the Arabic system of medicine was in use. He wrote also on jurisprudence a text-book of the law of inheritance, which is still extant in MS., and also produced works on astronomy and grammar. He maintained that the task of philosophy was one approved and commended by religion, for the Qur´an shows that God commands men to search for the truth. It is only the prejudice of the unenlightened which fears freedom of thought, because for those whose knowledge is imperfect the truths of philosophy seem to be contrary to religion. On this topic he composed two theological treatises--“On the Agreement of Religion with Philosophy” and “On the Demonstration of Religious Dogmas,” both of which have been edited by M. J. Mueller. The popular beliefs he does not accept, but he regards them as wisely designed to teach morality and to develop piety amongst the people at large; the true philosopher allows no word to be uttered against established religion, which is a thing necessary for the welfare of the people. Aristotle he regards as the supreme revelation of God to man: with it religion is in total agreement, but as religion is known to the multitude it only partially discloses Divine truth and adapts it to the practical needs of the many; in religion there is a literal meaning, which is all the uneducated are able to attain, and there is an “interpretation,” which is the disclosing of deeper truths beneath the surface which it is not expedient to communicate to the multitude. He opposes the position of Ibn Bajja, who inclined to solitary meditation and avoided the discussion of philosophical problems; he admits and desires such discussion provided it is confined to the educated who are able to understand its bearing, and not brought before the multitude who are thereby in danger of having their simple faith undermined. He agrees with Ibn Bajja, however, as against Ibn Tufayl in disapproval of ecstasy; such a thing may be, but it is too rare to need serious consideration.