Although a follower of Voltaire's deist beliefs early in his life, Denis Diderot became an ardent atheist and a believer in materialism, the view that the fundamental substance that makes up the whole of nature is matter and that material interactions produce all phenomena, even human thought and consciousness. He was a deep skeptic and a humanist, who warned against the assumption that knowledge and technology were automatically progressive.
Denis Diderot was a writer, philosopher and art critic during the Enlightenment and shared many similar views with other thinkers of the period. Diderot's ideas, however, were more progressive than those of most of his contemporaries. His views earned him a scandalous reputation as a freethinker and an atheist and even caused him to spend three months in jail. At the heart of Diderot's ideas was skepticism and the need to question everything, which he claimed was the only path toward truth. Such methods of thought led him to assert that every individual is deserving of both physical and intellectual freedom from authorities of any kind in the interest of the common good. He disliked the concept of freedom for hedonistic pleasures alone.
Diderot's "Encyclopédie," an encyclopedia that he hoped would contain all the information in the world, was his most famous accomplishment during his lifetime. He believed that knowledge of all things, whether arts, science or otherwise, should be available to the public rather than monopolized by academics, politicians or clergy. The "Encyclopédie" was banned twice in Paris, but Diderot still published abroad, where many libraries put the tome on display and often allowed ordinary citizens to use it.