Why is language the most important element in Humboldt’s thought? The key lies in Humboldt’s response to a central paradox in the idea of enlightenment, of which the best-known formulation is Kant’s famous essay What is Enlightenment?

In that essay, written in response to a theme set by the Prussian academy in 1784, Kant resoundingly defines enlightenment as “humanity leaving behind its own self-incurred immaturity” (der Ausgang des Menschen aus seiner selbstverschuldeten Unmündigkeit) and its motto as “Have the courage to use your own understanding!” (Habe Mut, Dich Deines eigenen Verstandes zu bedienen!). For Kant, this is an imperative to be liberated from the tutelage of intellectual guardians who tell us how to think, priests who tell us what to believe, doctors who tell us what to eat, and soldiers who tell us only to obey. The freedom he enjoins us to realize is logically negative: it is freedom from the constraint of authority external to ourselves, not the freedom to attain any specific object that Kant wants to define. Yet its consequences are far-reaching and of great political and social import. First, it is worth noticing that Kant’s idea of maturity (“Mündigkeit”) has a double meaning. As the adjective “self-incurred” (selbstverschuldet) suggests, it clearly means the intellectual or psychological immaturity that is our own fault, because we lack the courage to emancipate ourselves from it. However, it also means the legally defined and enforced condition of majority and its opposite (“Unmündigkeit”), the status of a minor, who has tutors or guardians (“Vormünder”; ibid., 453) set over him or her. The two meanings are linked by Kant’s assertion that many people, having reached the age of adulthood, behave as if they were still minors because they voluntarily accept the tutelage imposed on them.

In the course of Kant’s essay, it becomes clear that this dual emphasis has social and political as well as intellectual consequences. If Kant’s argument was only about the idea of enlightenment, then our failure to realize that idea could only be a consequence of a lack of knowledge or courage. Once we had understood the imperative to use our own understanding, it would simply be up to us—Kant’s original or modern readers—to carry it out in reality: the actual social and political world.