J.R.R. Tolkien’s 1931 essay about his invented languages was titled A Secret Vice.
In the essay, Tolkien discusses the pleasure of constructing languages and explains why a private language can become artistically meaningful. He connects language invention with mythology, imagination, and the human desire to create systems of sound and meaning.
The title reflects Tolkien’s description of language creation as a personal hobby that many people might not understand. The essay is especially valuable because it reveals Tolkien’s linguistic ideas directly, rather than only through the fictional languages appearing in his stories. It also helps explain why invented speech was central to the structure of his legendarium.