“We do not know nature at all; causes hidden deep within her may have produced everything. Look in your turn at Trembley’s polyp! Does it not contain inside it the causes of its own regeneration? Why then would it be absurd to believe that there exist physical causes for which everything was made and to which the whole chain of this vast universe is so necessarily linked and subordinated that nothing that happens could not have happened; that it is our absolutely invincible ignorance of these causes that has made us look to a god, who is not even a being of reason, according to some? Thus, destroying chance does not mean proving the existence of a supreme being, for there may be something else which is neither chance nor god; I mean ‘nature’, the study of which can as a result only produce unbelievers, as is proved by the manner of thinking of all its most successful observers.”

— Denis Diderot (c.1745), Philosophical Thoughts; cited by Julien la Mettrie (1747) in Man: a Machine (pg. 24)

“If you want me to believe in god, you must make me touch him.”

— Denis Diderot (1749), portrayal of fictional conversation of Nicholas Saunderson with a priest, in Letters of the Blind (Ѻ)

“I believe in god, but I also live happily with atheists. It is very important not to mistake hemlock for parsley; but not at all so to believe or not in god.”

— Denis Diderot (c.1765), “Response to Voltaire” (Ѻ); note: in his Diderot-Barthelemy dialogue (1773), Diderot states that he said this "I believe in god" statement only to flatter Voltaire, and when on to state correctly that he was an "unbeliever". [4]

“He knows nothing, but nothing of what he has done, and I see this man—machine pure and simple—experiencing different motives which have impelled it without having freed it; it has not produced a single expressly voluntary act.”

“I have read with extreme pleasure your book [Letter on the Blind, 1749]. I am concerned with the absence of an ‘infinitely cleaver workman’ in your universe? I desire passionately to converse with you, no matter whether you think you are one of his works or whether you think you are a necessarily organized portion of an eternal and necessary matter.”

— Voltaire (c.1749), “Letter to Denis Diderot” [8]

“Vartanian (Ѻ), as many critics do, believes that in 1746 Diderot truly was a deist: he prefaced the Philosophic Letters with ‘I write about god.’ Soon Spinozism (the notion that god and the universe are one and the same and that god does not exist outside the universe) replaced Diderot's deism. However, by 1749, La Mettrie's materialism convinced Diderot to embrace atheism. When Diderot sat down to write the Letter on the Blind in 1749, atheism had replaced Spinozism. Vartanian says that Diderot embraced ‘Nature capitalized . . . and endowed with several of the creative powers formerly reserved to god.’ Vartanian points out that La Mettrie, who in Man machine, published a year before the Letter on the Blind, declared: "Let us not limit the resources of nature; they are infinite’.”

— Mary Gregory (2007), Diderot and the Metamorphosis of Species (pg. 83)

“The philosopher has never killed any priests, whereas the priest has killed a great many philosophers.”

— Denis Diderot (c.1770) [3]

“Skepticism is the first step on the road to philosophy.”

— Dennis Diderot (c.1770) (Ѻ)

“Man will never be free until the last king is strangled with the entrails of the last priest.”

— Dennis Diderot (c.1770) (Ѻ); paraphrase (or mis-attribution) of Jean Meslier

“There are three principal means of acquiring knowledge: observation of nature, reflection, and experimentation. Observation collects facts; reflection combines them; experimentation verifies the result of that combination.”

— Dennis Diderot (c.1770) (Ѻ)

“Pithy sentences are like sharp nails which force truth upon our memory.”

— Dennis Diderot (c.1770) (Ѻ)

“There are things I can't force. I must adjust. There are times when the greatest change needed is a change of my viewpoint.”

— Dennis Diderot (c.1770) (Ѻ)

“Only passions, great passions can elevate the soul to great things.”

— Dennis Diderot (c.1770) (Ѻ)

“Lost in an immense forest during the night I only have a small light to guide me. An unknown man appears and says to me: ‘my friend, blow out your candle so you can better find your way.’ This unknown man is a theologian.”

— Denis Diderot (c.1770), “Thoughts on Religion” [7]