Thus, in Islam, a whole system, which could not even pretend to draw its authority from the Sunnah, had come to be accepted.  It was not difficult to justify this deviation from the orthodox abhorrence against novelties.  Islam has always looked at the world in a pessimistic way, a view expressed in numberless prophetic sayings.  The world is bad and will become worse and worse.  Religion and morality will have to wage an ever more hopeless war against unbelief, against heresy and ungodly ways of living.  While this is surely no reason for entering into any compromise with doctrines which depart but a hair’s breadth from Qoran and Sunnah, it necessitates methods of defence against heresy as unknown in Mohammed’s time as heresy itself.  “Necessity knows no law” is a principle fully accepted in Islam; and heresy is an enemy of the faith that can only be defeated with dialectic weapons.  So the religious truths preached by Mohammed have not been altered in any way; but under the stress of necessity they have been clad in modern armour, which has somewhat changed their aspect.

Moreover, Islam has a theory, which alone is sufficient to justify the whole later development of doctrine as well as of law.  This theory, whose importance for the system can hardly be overestimated, and which, nevertheless, has until very recent times constantly been overlooked by Western students of Islam, finds its classical expression in the following words, put into the mouth of Mohammed:  “My community will never agree in an error.”  In terms more familiar to us, this means that the Mohammedan Church taken as a whole is infallible; that all the decisions on matters practical or theoretical, on which it is agreed, are binding upon its members.  Nowhere else is the catholic instinct of Islam more clearly expressed.

A faithful Mohammedan student, after having struggled through a handbook of law, may be vexed by a doubt as to whether these endless casuistic precepts have been rightly deduced from the Qoran and the Sacred Tradition.  His doubt, however, will at once be silenced, if he bears in mind that Allah speaks more plainly to him by this infallible Agreement (Ijma’) of the Community than through Qoran and Tradition; nay, that the contents of both those sacred sources, without this perfect intermediary, would be to a great extent unintelligible to him.  Even the differences between the schools of law may be based on this theory of the Ijma’; for, does not the infallible Agreement of the Community teach us that a certain diversity of opinion is a merciful gift of God?  It was through the Agreement that dogmatic speculations as well as minute discussions about points of law became legitimate.  The stamp of Ijma’ was essential to every rule of faith and life, to all manners and customs.

All sorts of religious ideas and practices, which could not possibly be deduced from Mohammed’s message, entered the Moslim world by the permission of Ijma’.  Here we need think only of mysticism and of the cult of saints.