Tisdall's classic work explores the sources from which Muhammad borrowed the ideas and narratives and precepts he has incorporated into the religion he founded. Which of these were his own invention, which of them were derived from earlier systems? To what extent had he the means of learning the teachings of those who professed other religions than his own? If he borrowed from other systems, what particular parts of the Qu'ran can be traced to such sources? How much of the Qur'an is due to the character of Muhammad himself and the circumstances of his time?