Euler insisted that knowledge is founded in part on the basis of precise quantitative laws, something that monadism and Wolffian science were unable to provide. Euler's religious leanings might also have had a bearing on his dislike of the doctrine; he went so far as to label Wolff's ideas as "heathen and atheistic".
Much of what is known of Euler's religious beliefs can be deduced from his Letters to a German Princess
and an earlier work, Rettung der Göttlichen Offenbahrung Gegen die Einwürfe der Freygeister
(Defense of the Divine Revelation against the Objections of the Freethinkers
). These works show that Euler was a devout Christian
who believed the Bible to be inspired; the Rettung
was primarily an argument for the divine inspiration of scripture
There is a famous anecdote inspired by Euler's arguments with secular philosophers over religion, which is set during Euler's second stint at the St. Petersburg academy. The French philosopher Denis Diderot
was visiting Russia on Catherine the Great's invitation. However, the Empress was alarmed that the philosopher's arguments for atheism
were influencing members of her court, and so Euler was asked to confront the Frenchman. Diderot was later informed that a learned mathematician had produced a proof of the existence of God
: he agreed to view the proof as it was presented in court. Euler appeared, advanced toward Diderot, and in a tone of perfect conviction announced, "Sir,
, hence God exists—reply!". Diderot, to whom (says the story) all mathematics was gibberish, stood dumbstruck as peals of laughter erupted from the court. Embarrassed, he asked to leave Russia, a request that was graciously granted by the Empress. However amusing the anecdote may be, it is apocryphal
, given that Diderot was a capable mathematician who had published mathematical treatises.