In 1784, Immanuel Kant published a short essay under the title, What is Enlightenment? Kant's answer to his own question was stated, seemingly without hesitation, at the very outset of the work:

While the placing of this definition both guaranteed its prominence and, to an extent, exemplified the author's own bold self-reliance, it also allowed Kant to go on, in the remainder of the essay, to complicate his prompt answer to the initial question. Indeed, the definition duly makes way for somewhat looser, less definite conclusions. Kant ultimately provided a delicately balanced assessment by arguing that eighteenth-century men and women were living in an age of Enlightenment, but not an enlightened age.

Many of Kant's intellectual contemporaries and his immediate antecedents in France, of whom he was highly aware, were, however, inclined to think, or at least write, that theirs was an enlightened age – ‘un’ or ‘ce siècle éclairé’. Indeed, such was the frequency with which these words came together that by the 1750s the happy designation had already hardened into a cliché. The antiquarian and art historian, the Comte de Caylus observed that these magical words were bandied about at the drop of a hat: ‘Quoiqu’ on dise à tout propos, dans un siècle aussi éclairé que le nôtre, on peut assurer que la race des barbares n'est pas encore éteinte’ (‘Although at every juncture people say in a century as enlightened as ours, you can be assured that the barbarians are still with us’).