In the wake of the great revolution of the sixteenth century, when the critical spirit had applied itself to the task of distinguishing false from true among the various Christian traditions, bolder and more curious minds had repeatedly dared to contest or reject all of them. The same spirit that had led millions of Catholics to abandon Catholicism in Luther's time impelled a few individual Christians every year to abandon Christianity itself: unbelief followed heresy.

In general terms it is safe to say that by the eighteenth century, Christianity had lost much of its power throughout Europe. In most countries, however, it was neglected rather than violently combated. Even those countries that abandoned religion did so almost regretfully. Irreligion was widespread among princes and clever wits but had yet to penetrate deeply into the middle and lower classes. It was still an intellectual caprice, not a common opinion. In 1787, Mirabeau said that “it is widely believed in Germany that the Prussian provinces are full of atheists. The truth is that although some freethinkers can be found there, the common people are as devoted to religion as in the most devout countries, and indeed there is no shortage of fanatics.” It was deeply to be regretted, moreover, that Frederick II had not authorized the marriage of Catholic priests and, even more, that he had refused to allow those who did marry to keep the income from their benefices, “a measure, I daresay, that would have been worthy of that great man.”