Hence, it is necessary for the doctors of Islam to prevent men, except the learned, from reading his books; as it is incumbent upon them to hinder them from reading controversial writings which should not be studied except by those fit to do so. As a rule the reading of these books is less harmful than those of the former. For the majority cannot understand philosophical books, only those endowed with superior natures. People are on the whole destitute of learning and are aimless in their reading which they do without a teacher. Nevertheless they succeed in leading others away from religion. It is an injustice to the best kind of men and the best kind of creation; for in their case justice consists in the knowledge of the best things by the best people, fit to know it. It should be remembered that the greater the thing is the higher will be the injustice done to it on account of ignorance. Hence God says: “Polytheism is a great injustice.”[17] These things we have thought proper to mention here, that is, in a discussion of the relation between philosophy and religion and the canons of interpretation in Law. If these matters had not become commonly known among men, we would not have said anything about them and would not have entered in a plea on behalf of the interpreters. For these things are suitable only for mention in philosophical books. You ought to be aware that the real purpose of the Law is to impart the knowledge of truth and of right action. The knowledge of truth consists in the cognisance of God and the whole universe with its inner significance, especially that of religion, and the knowledge of happiness or misery of the next world. Right action consists in following those actions which are useful for happiness and avoiding those which lead to misery. The knowledge of these actions has been called practical knowledge. This is divided into two kinds: external actions, the knowledge of which is called Fiqh, that is, Theology; and actions pertaining to feelings, such as gratitude, patience, and other points of character to which the Law has urged us or from which it has prohibited us. This is called the knowledge of continence and of the next world. Abu Hamid in his book _The Revivification of the Sciences of Religion_ seems to be inclined to this kind, and as the people have always turned away from the former kind of knowledge and have turned themselves to the second which leads them easily to piety, the book attained its name. But we have wandered from our own purpose and will now return to it.