"The Invisible Libertine" is a concept developed by French philosopher Pierre Bayle (1647-1706) in his work "Dictionnaire historique et critique" (1697). Bayle was a prominent figure in the Enlightenment, known for his critical thinking and skeptical views.

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The concept of the invisible libertine has been influential in the history of philosophy, particularly in the development of modern skepticism and critical thinking. Bayle's ideas have inspired thinkers such as Immanuel Kant, Voltaire, and David Hume.

In his article "Le Libertin Invisible" (The Invisible Libertine), Bayle described a type of person who, despite appearing to be a devout Christian, secretly holds libertine (free-thinking) views. These individuals would often use their outward conformity to societal norms to conceal their true, more radical ideas.