As to the other characteristics of inspiration, they are only revealed to adepts in Sufism and in a state of ecstatic transport. The little that we know of the nature of inspiration we owe to the kind of likeness to it which we find in sleep; without that we should be incapable of comprehending it, and consequently of believing in it, for conviction results from comprehension. The process of initiation into Sufism exhibits this likeness to inspiration from the first. There is in it a kind of ecstasy proportioned to the condition of the person initiated, and a degree of certitude and conviction which cannot be attained by reason. This single fact is sufficient to make us believe in inspiration. We now come to deal with doubts relative to the inspiration of a particular prophet. We shall not arrive at certitude on this point except by ascertaining, either by ocular evidence or by reliable tradition, the facts relating to that prophet. When we have ascertained the real nature of inspiration and proceed to the serious study of the Koran and the traditions, we shall then know certainly that Muhammed is the greatest of prophets. After that we should fortify our conviction by verifying the truth of his preaching and the salutary effect which it has upon the soul. We should verify in experience the truth of sentences such as the following: “He who makes his conduct accord with his knowledge receives from God more knowledge”; or this, “God delivers to the oppressor him who favours injustice”; or again, “Whosoever when rising in the morning has only one anxiety (to please God), God will preserve him from all anxiety in this world and the next.”