In Montesquieu’s time people were under the illusion that legislation has an almost unlimited power to modify social conditions.  We have seen this in the case of Saint-Pierre.  Montesquieu’s conception of general laws should have been an antidote to this belief.  It had however less effect on his contemporaries than we might have expected, and they found more to their purpose in what he said of the influence of laws on manners.  There may be something in Comte’s suggestion that he could not give his conception any real consistency or vigour, just because he was himself unconsciously under the influence of excessive faith in the effects of legislative action.

A fundamental defect in Montesquieu’s treatment of social phenomena is that he abstracted them from their relations in time.  It was his merit to attempt to explain the correlation of laws and institutions with historical circumstances, but he did not distinguish or connect stages of civilisation.  He was inclined to confound, as Sorel has observed, all periods and constitutions.  Whatever be the value of the idea of Progress, we may agree with Comte that, if Montesquieu had grasped it, he would have produced a more striking work.  His book announces a revolution in the study of political science, but in many ways belongs itself to the pre-Montesquieu era.

2.

In the same years in which Montesquieu was busy on the composition of the Esprit des lois, Voltaire was writing his Age of Louis XIV. and his Essay on the Manners and Mind of Nations, and on the Principal Facts of History from Charlemagne to the Death of Louis XIII.  The former work, which everybody reads still, appeared in 1751.  Parts of the Essay, which has long since fallen into neglect, were published in the Mercure de France between 1745 and 1751; it was issued complete in 1756, along with the Age of Louis XIV., which was its continuation.  If we add the Precis of the Reign of Louis xv. (1769), and observe that the Introduction and first fourteen chapters of the Essay sketch the history of the world before Charlemagne, and that China, India, and America are included in the survey, Voltaire’s work amounts to a complete survey of the civilisation of the world from the earliest times to his own.  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.”