"The System of Nature" is a long and extensive work presenting a thoroughly naturalistic view of the world. Some d'Holbach scholars have pointed out that Denis Diderot was a close personal friend of d'Holbach's, and that it is unclear to what extent d'Holbach was influenced by him. Indeed, Diderot may possibly have been the author of parts of the "System of Nature". Regardless, however, of the extent of Diderot's contribution to the "System of Nature", it is on the basis of this work that d'Holbach's philosophy has been called "the culmination of French materialism and atheism."