A philosopher argued the whole universe, including your thoughts, is just matter in motion

In 1770, Baron d'Holbach anonymously published 'The System of Nature,' arguing everything that exists — thought, will and morality included — is just matter obeying natural law, with no soul, no free will beyond physical causes, and no God needed to explain any of it. The book caused a scandal across Europe, was publicly burned by the French government, and was deemed too radical even by fellow skeptics like Voltaire, who wrote a rebuttal despite sharing Holbach's distaste for religion.

— Baron d'Holbach (published anonymously), Systeme de la Nature (The System of Nature) — 1770