His System of Nature (1770) develops a purely naturalistic theory of the universe, in which the prevalent Deism is rejected: there is no God; material Nature stands out alone, self-sufficing, dominis privata superbis.

The book suggests how the Lucretian theory of development might have led to the idea of Progress.

But it sent a chilly shock to the hearts of many and probably convinced few.

The effective part was the outspoken and passionate indictment of governments and religions as causes of most of the miseries of mankind.
It is in other works, especially in his Social System, that his views of Progress are to be sought.

Man is simply a part of nature; he has no privileged position, and he is born neither good nor bad.