Central to this complex is Voltaire’s conception of liberty. Around this category, Voltaire’s social activism and his relatively rare excursions into systematic philosophy also converged. In 1734, in the wake of the scandals triggered by the Lettres philosophiques, Voltaire wrote, but left unfinished at Cirey, a Traité de metaphysique that explored the question of human freedom in philosophical terms. The question was particularly central to European philosophical discussions at the time, and Voltaire’s work explicitly referenced thinkers like Hobbes and Leibniz while wrestling with the questions of materialism, determinism, and providential purpose that were then central to the writings of the so-called deists, figures such as John Toland and Anthony Collins. The great debate between Samuel Clarke and Leibniz over the principles of Newtonian natural philosophy was also influential as Voltaire struggled to understand the nature of human existence and ethics within a cosmos governed by rational principles and impersonal laws.