D'Holbach wrote and published this book – possibly with the assistance of Denis Diderot[1] but with the support of Jacques-André Naigeon – anonymously in 1770, describing the universe in terms of the principles of philosophical materialism: the mind is identified with the brain, there is no "soul" without a living body, the world is governed by strict deterministic laws, free will is an illusion,[2] there are no final causes, and whatever happens takes place because it inexorably must.

It makes a critical distinction between mythology as a more or less benign way of bringing law-ordered thought on society, nature and their powers to the masses and theology.

Voltaire, too, seized his pen to refute the philosophy of the Système in the article "Dieu" in his Dictionnaire philosophique, while Frederick the Great also drew up an answer to it.

[4] Commenting on the book, Frederick observed: When one speaks in public he should consider the delicacy of superstitious ears; he should not shock anybody; he should wait till the time is sufficiently enlightened to let him think out loud.

[8] In his student days, Goethe had recoiled with revulsion at the contents in the book: "It appeared to us so grey, so Cimmerian, so corpse – like that we had difficulty in enduring its presence and shuddered before it as before a spectre"; in his old age he harbored similar views: "We belong to the laws of nature, even when we rebel against them.