All the successive inventions of the human mind to change or perfect man's mode of existence and render it happier were only the necessary consequence of his essence and that of the existences which act upon him. All we do or think, all we are or shall be, is only an effect of what universal nature has made us. Art is only nature acting by the aid of the instruments which she has fashioned. [Footnote: The passages of d'Holbach specially referred to are: Systeme social, i. 1, p. 13; Syst. de la nature, i. 6, p. 88; Syst. soc. i. 15, p. 271; Syst. de la n. i. 1, p. 3.] Progress, therefore, is natural and necessary, and to criticise or condemn it by appealing to nature is only to divide the house of nature against itself. If d'Holbach had pressed his logic further, he would have taken a more indulgent and calmer view of the past history of mankind. He would have acknowledged that institutions and opinions to which modern reason may give short shrift were natural and useful in their day, and would have recognised that at any stage of history the heritage of the past is no less necessary to progress than the solvent power of new ideas. Most thinkers of his time were inclined to judge the past career of humanity anachronistically. All the things that had been done or thought which could not be justified in the new age of enlightenment, were regarded as gratuitous and inexcusable errors. The traditions, superstitions, and customs, the whole "code of fraud and woe" transmitted from the past, weighed then too heavily in France to allow the school of reform to do impartial justice to their origins. They felt a sort of resentment against history. D'Alembert said that it would be well if history could be destroyed; and the general tendency was to ignore the social memory and the common heritage of past experiences which mould a human society and make it something very different from a mere collection of individuals. Belief in Progress, however, took no extravagant form. It did not beguile d'Holbach or any other of the leading thinkers of the Encyclopaedia epoch into optimistic dreams of the future which might await mankind. They had a much clearer conception of obstacles than the good Abbe de Saint-Pierre. Helvetius agrees with d'Holbach that progress will be slow, and Diderot is wavering and sceptical of the question of indefinite social improvement. [Footnote: De l'esprit, Disc. ii. cc. 24, 25.] 6.