Even before I saw The Favourite, I knew from an outline of the plot that I had heard some of the characters’ names at an early age – thanks to a performance of Le Verre d’eau by Eugène Scribe. Neither the film nor the play aimed at historical accuracy, of course: Lanthimos probably wanted as little of it as possible and Scribe didn’t care much for veracity.
In The Historical and Dramatic Sources of Scribe’s Verre d’Eau (1958) Colin Duckworth inquired whether Scribe had picked the plot from Voltaire, specifically from an anecdote related in Le siècle de Louis XIV (1751). Duckworth argued that Voltaire’s influence on Scribe was primarily the “small cause, large effect” theory that inspired the playwright: the full title of the once-famous play is Le Verre d’eau, ou, Les Effets et les causes.
According to The Cambridge Companion to Voltaire, the philosopher wrote to Friedrich II as early as in 1738:
If the Duchess of Marlborough had not spilt a bowl of water in front of Lady Masham, and a few drops on Queen Anne, Queen Anne would not have thrown herself at the Torys [here the translator left unchanged Voltaire’s French plural] and would not have given France the peace which it needed to survive.
An abridged (I think) translation of The Age of Louis XIV, by William Fleming, can be found here. The story of downfall of the Marlboroughs and the brief (1710-14) Tory ascendancy begins with this exposition:
Sarah Jennings, duchess of Marlborough, governed Queen Anne, and the duke, her husband, governed the state. He had the treasury at his command, through the means of the lord high treasurer, Godolphin, whose son had married one of his daughters. His son-in-law, Sunderland, who was secretary of state, submitted everything in the cabinet to him, and the queen’s household, where his wife had an unlimited authority, was at his devotion. He was master of the army, while he had the disposal of all offices.
In his Philosophical Dictionary (1764), as in the 1734 letter, Voltaire uses this example in support of his theory of causality. He starts by citing one of the major actors on the British political scene during the second half of Anne’s reign:
Lord Bolingbroke acknowledges that he was indebted to the petty quarrels between the duchess of Marlborough and Mrs. Masham for an opportunity of concluding the private treaty between Queen Anne and Louis XIV.
Voltaire’s source for this was likely Henry St. John, viscount Bolingbroke, himself. They must have first met in France in the early 1720s.