If Montesquieu founded social science, Voltaire created the history of civilisation, and the Essay, for all its limitations, stands out as one of the considerable books of the century.
In his Age of Louis XIV.

he announced that his object was "to paint not the actions of a single man, but the mind of men (l'esprit des hommes) in the most enlightened age that had ever been," and that "the progress of the arts and sciences" was an essential part of his subject.

In the same way he proposed in the Essay to trace "l'histoire de l'esprit humain," not the details of facts, and to show by what steps man advanced "from the barbarous rusticity" of the times of Charlemagne and his successors "to the politeness of our own." To do this, he said, was really to write the history of opinion, for all the great successive social and political changes which have transformed the world were due to changes of opinion.

Prejudice succeeded prejudice, error followed error; "at last, with time men came to correct their ideas and learn to think." The motif of the book is, briefly, that wars and religions have been the great obstacles to the progress of humanity, and that if they were abolished, with the prejudices which engender them, the world would rapidly improve.
"We may believe," he says, "that reason and industry will always progress more and more; that the useful arts will be improved; that of the evils which have afflicted men, prejudices, which are not their least scourge, will gradually disappear among all those who govern nations, and that philosophy, universally diffused, will give some consolation to human nature for the calamities which it will experience in all ages." This indeed is not the tone of the Abbe de Saint-Pierre.

Voltaire's optimism was always tempered with cynicism.