379.] It is impossible, he says, to compare two states of society and determine that in one more happiness was enjoyed than in the other.

The happiness of an individual requires a certain degree of harmony between his faculties and his environment.

But there is always a natural tendency towards the establishment of such an equilibrium, and there is no means of discovering by argument or by direct experience the situation of a society in this respect.

Therefore, he concludes, the question of happiness must be eliminated from any scientific treatment of civilisation.
Chastellux won a remarkable success.

His work was highly praised by Voltaire, and was translated into English, Italian, and German.
It condensed, on a single issue, the optimistic doctrines of the philosophers, and appeared to give them a more solid historical foundation than Voltaire's Essay on Manners had supplied.