Islam
Voltaire's views about Islam were generally negative, and he found its holy book, the Quran, to be ignorant of the laws of physics. In a 1740 letter to Frederick the Great, Voltaire ascribes to Muhammad a brutality that "is assuredly nothing any man can excuse" and suggests that his following stemmed from superstition. Voltaire continued, "But that a camel-merchant should stir up insurrection in his village; that in league with some miserable followers he persuades them that he talks with the angel Gabriel; that he boasts of having been carried to heaven, where he received in part this unintelligible book, each page of which makes common sense shudder; that, to pay homage to this book, he delivers his country to iron and flame; that he cuts the throats of fathers and kidnaps daughters; that he gives to the defeated the choice of his religion or death: this is assuredly nothing any man can excuse, at least if he was not born a Turk, or if superstition has not extinguished all natural light in him."
In 1748, after having read Henri de Boulainvilliers and George Sale, he wrote again about Mohammed and Islam in "De l'Alcoran et de Mahomet" ("On the Quran and on Mohammed"). In this essay, Voltaire maintained that Mohammed was a "sublime charlatan". Drawing on complementary information in Herbelot's Bibliothèque orientale ('Oriental Library'), Voltaire, according to René Pomeau, adjudged the Quran, with its "contradictions, ... absurdities, ... anachronisms", to be "rhapsody, without connection, without order, and without art".
Thus he "henceforward conceded" that "if his book was bad for our times and for us, it was very good for his contemporaries, and his religion even more so. It must be admitted that he removed almost all of Asia from idolatry" and that "it was difficult for such a simple and wise religion, taught by a man who was constantly victorious, could hardly fail to subjugate a portion of the earth." He considered that "its civil laws are good; its dogma is admirable which it has in common with ours" but that "his means are shocking; deception and murder".
In his Essay on the Manners and Spirit of Nations (published 1756), Voltaire deals with the history of Europe before Charlemagne to the dawn of the age of Louis XIV, and that of the colonies and the East. As a historian, he devoted several chapters to Islam, He highlighted the Arabian, Turkish courts, and conducts. Here he called Mohammed a "poet", and stated that he was not an illiterate. As a "legislator", he "changed the face of part of Europe [and] one half of Asia."
In chapter VI, Voltaire finds similarities between Arabs and ancient Hebrews, that they both kept running to battle in the name of God, and sharing a passion for the spoils of war. Voltaire continues that, "It is to be believed that Mohammed, like all enthusiasts, violently struck by his ideas, first presented them in good faith, strengthened them with fantasy, fooled himself in fooling others, and supported through necessary deceptions a doctrine which he considered good." He thus compares "the genius of the Arab people" with "the genius of the ancient Romans".
According to Malise Ruthven, as Voltaire learned more about Islam, his opinion of the faith became more positive. As a result, his play Mahomet inspired Goethe, who was attracted to Islam, to write a drama on this theme, though he completed only the poem "Mahomets-Gesang" ("Mahomet's Singing").
The tragedy Fanaticism, or Mahomet the Prophet (French: Le fanatisme, ou Mahomet le Prophete) was written in 1736 by Voltaire. The play is a study of religious fanaticism and self-serving manipulation. The character Muhammad orders the murder of his critics. Voltaire described the play as "written in opposition to the founder of a false and barbarous sect."
Voltaire described Muhammad as an "impostor", a "false prophet", a "fanatic" and a "hypocrite". Defending the play, he said that he "tried to show in it into what horrible excesses fanaticism, led by an impostor, can plunge weak minds". When Voltaire wrote in 1742 to César de Missy, he described Muhammad as deceitful.
In his play, Muhammad is "whatever trickery can invent that is most atrocious and whatever fanaticism can accomplish that is most horrifying. Mahomet here is nothing other than Tartuffe with armies at his command." After later having judged that he had made Muhammad in his play "somewhat nastier than he really was", Voltaire claimed that Muhammad stole the idea of an angel weighing both men and women from Zoroastrians, who are often referred to as "Magi". Voltaire continued about Islam, saying:
Nothing is more terrible than a people who, having nothing to lose, fight in the united spirit of rapine and of religion.
In a 1745 letter recommending the play to Pope Benedict XIV, Voltaire described Muhammad as "the founder of a false and barbarous sect" and "a false prophet". Voltaire wrote: "Your holiness will pardon the liberty taken by one of the lowest of the faithful, though a zealous admirer of virtue, of submitting to the head of the true religion this performance, written in opposition to the founder of a false and barbarous sect. To whom could I with more propriety inscribe a satire on the cruelty and errors of a false prophet, than to the vicar and representative of a God of truth and mercy?" His view was modified slightly for Essai sur les Moeurs et l'Esprit des Nations, although it remained negative. In 1751, Voltaire performed his play Mohamet once again, with great success.