CHAPTER IV THE EIGHTEENTH CENTURY In so far as the intellectual climates of different epochs can be contrasted, the eighteenth century in Europe was the complete antithesis to the Middle Ages. The contrast is symbolised by the difference between the cathedral of Chartres and the Parisian salons, where D’Alembert conversed with Voltaire. The Middle Ages were haunted with the desire to rationalise the infinite: the men of the eighteenth century rationalised the social life of modern communities, and based their sociological theories on an appeal to the facts of nature. The earlier period was the age of faith, based upon reason. In the later period, they let sleeping dogs lie: it was the age of reason, based upon faith. To illustrate my meaning:—St. Anselm would have been distressed if he had failed to find a convincing argument for the existence of God, and on this argument he based his edifice of faith, whereas Hume based his _Dissertation on the Natural History of Religion_ upon his faith in the order of nature. In comparing these epochs it is well to remember that reason can err, and that faith may be misplaced. In my previous lecture I traced the evolution, during the seventeenth century, of the scheme of scientific ideas which has dominated thought ever since. It involves a fundamental duality, with _material_ on the one hand, and on the other hand _mind_. In between there lie the concepts of life, organism, function, instantaneous reality, interaction, order of nature, which collectively form the Achilles heel of the whole system.