In this letter, Voltaire playfully tells a lady that although she may not care much for metaphysics, it is amusing to ponder whether the soul exists. He jokes that, like a Swiss captain praying before battle, people hedge their bets about God and the soul. He doubts she will find his writings entertaining, as she is too learned and reflective, but sends her a few chapters anyway — entries on alchemists, the Koran, and Alexander — hoping they might amuse her briefly. Voltaire praises her grandmother as a true philosopher who prefers doing good for her people in her quiet estate of Amboise to the empty noise of courtly life. He imagines her wise, gentle, charitable, and modestly virtuous. He also mentions having sent her some of his watchmaking experiments under her protection and laments local shortages of grain. Turning to politics, he predicts that the Russians will soon conquer the Turks — an unexpected revolution, he says, to test her grandmother’s philosophy — while his own is simply to endure patiently.

The writer reflects on the futility and effort of their work, comparing it to insects that live briefly after long preparation, and urges the recipient to consider their article on ‘Ancients and Moderns’ as a matter of taste. They discuss the value of scientific knowledge despite its complexity and highlight their own role in supporting a colony established with the aid of Madame la Duchesse de Choiseul. Additionally, they mention sending a legal memorandum related to Franche-Comté, expressing frustration with ecclesiastical and feudal systems, and reaffirm their resignation to the world’s fate while cherishing the friendship of the recipient.

Voltaire discusses his views on metaphysics in response to Louis-Martin Kahle (1712-1775), professor and dean of the Faculty of Philosophy in Göttingen and makes a brief mention his encounter with Sir Isaac Newton in England. Voltaire had published Métaphysique de Newton in 1740, a text which would later form the first part of his Elements de la philosophie de Newton. Voltaire writes that he had been much criticised by some German doctors and his ‘Courte réponse’ is a reply to this criticism. The text ends with a passage in English which quotes John Milton’s Paradise Lost: ‘and reason’d high / of providence, fore knowledge, will, and fate: / fix’t fate, free will, fore knowledge absolute: / And foud non end, &c’ (l.558-61).

A letter of more than 2700 words from Frederick II, King of Prussia to Voltaire discussing his literary works and philosophical ideas. Frederick opens the letter by expressing his concerns about Voltaire’s frequent ill health. He has consulted doctors who have provided a long-range diagnosis, and he asks for a full statement of Voltaire’s symptoms. He then complains that Voltaire has added no criticised the poems he sent, and encloses revisions of two poems in response to Voltaire’s critiques, with a self-deprecating note on his incurable ‘mania’ for poetry, and an expression of admiration for Voltaire’s genius in rising above his physical weakness. Frederick expresses admiration for Voltaire’s ‘Épitre sur l’Envie’ and for his tragedy Mérope, offering his views on the role of love in modern theatre, and adding a verse encomium on the diversity of Voltaire’s achievements from history to science (citing his elucidation of Newton) to tragedy. Turning from literature to philosophy, the heart of the letter is a detailed consideration of some of the defining metaphysical debates of the Age of Enlightenment. Frederick expresses his scepticism at the arguments in favour of determinism, but declares himself concinced of the principle of ‘sufficient reason’ (that a rational cause lies behind every effect, and that in this sense ‘chance is the synonym of nothing’. He therefore argues that the true determinant of human actions is reason itself, and describes the idea of the deity which he deduces from this. In the last section of the letter, Frederick expresses mock-scepticism at the reported admiration for him of the Marquise du Châtelet, mentioning that he has discussed it with Leibniz, and joking that he now considers himself a rival of Newton’s for her favours.