The true interest of all these details about a mere book lies in the immense significance of the movement of political ideas and forces to which they belong.  The true interest of all history lies in the spectacle which it furnishes of the growth and dissolution, the shock and the transformation, incessantly at work among the great groups of human conceptions.  The decree against the Encyclopaedia marks the central moment of a collision between two antagonistic conceptions which disputed, and in France still dispute, with one another the shaping and control of institutions.  One of these ideas is the exclusion of political authority from the sphere and function of directing opinion; it implies the absolute secularisation of government.  The rival idea prompted the massacre of St. Bartholomew, the dragonnades, the revocation of the Edict of Nantes, and all the other acts of the same policy, which not only deprived France of thousands of the most conscientious and most ingenious of her sons, but warped and corrupted the integrity of the national conscience.  It is natural that we should feel anger at the arbitrary attempt to arrest Diderot’s courageous and enlightened undertaking.  Yet in truth it was only the customary inference from an accepted principle, that it is the business or the right of governments to guide thought and regulate its expression.  The Jesuits acted on this theory, and resorted to repressive power and the secular arm whenever they could.  The Jansenists repudiated the principle, but eagerly practised it whenever the turn of intrigue gave them the chance.

An extraordinary and unforeseen circumstance changed the external bearings of this critical conflict of ideas.  The conception of the duties of the temporal authority in the spiritual sphere had been associated hitherto with Catholic doctrine.  The decay of that doctrine was rapidly discrediting the conception allied with it.  But the movement was interrupted.  And it was interrupted by a man who suddenly stepped out from the ranks of the Encyclopaedists themselves.  Rousseau from his solitary cottage at Montmorency (1758) fulminated the celebrated letter to D’Alembert on Stage Plays.  The article on Geneva in the seventh volume of the Encyclopaedia had not only praised the pastors for their unbelief; it also assailed the time-honoured doctrine of the churches that the theatre is an institution from hell and an invention of devils.  D’Alembert paid a compliment to his patriarch and master at Ferney, as well as shot a bolt at his ecclesiastical foes in Paris, by urging the people of Geneva to shake off irrational prejudices and straightway to set up a playhouse.  Rousseau had long been brooding over certain private grievances of his own against Diderot; the dreary story has been told by me before, and happily need not be repeated.[146] He took the occasion of D’Alembert’s mischievous suggestion to his native Geneva, not merely to denounce the drama with all the force and eloquence at his command, but formally to declare the breach between himself and Diderot.  From this moment he treated the Holbachians—­so he contemptuously styled the Encyclopaedists—­as enemies of the human race and disseminators of the deadliest poisons.