In the language spoken by the Dothraki on the violent and popular HBO show Game of Thrones, the word for cat is keli. Reasonable, you might think. The show is based on the books written by George R.R. Martin, surely he can come up with whatever words he likes for the animals living in a universe he has dreamed up—that’s the fantasist’s prerogative. But Martin did not invent the word for the Dothraki cat. It’s named, in fact, after an individual real-world cat belonging to David J. Peterson, who has a web site which lists 13 separate languages of his own invention. Peterson has an M.A. in linguistics from the University of California, San Diego, and his bright blue, 1990s-chic web site has an alternate black-and-white version, in case you find it easier to read that way. Peterson is a conlanger, and he can do whatever he wants.

“Conlang” is short for “constructed language,” which is just what it sounds like: a language that has been constructed. There are a lot of them, of various sorts. International auxiliary languages like Volapük, Esperanto, or Interlingua are one specific type of conlang. Invented to facilitate international communication during the great techno-utopian-modernist thought-boom of the last two centuries, they never got terribly popular. Conlangs do not necessarily have to be useful. As Peterson explains in his new book The Art of Language Invention, conlanging is an art as well as a science, something you might do for your own pleasure, as well as for the entertainment of others. He is a conlanger for hire—besides Game of Thrones, Peterson has also worked on Syfy’s Defiance, in which humans and aliens coexist in postapocalyptic Missouri—an artist who will put words into the mouths of the characters, words which are part of a fully functioning language.

You might ask, “How long has this been a job, and may I have it?” Fortunately, The Art of Language Invention answers this question, for it is both a textbook for the amateur conlanger—a guide to inventing your own language spoken by aliens or squid or submarine antelope or whatever—and a brief history of conlanging itself. And the story of conlanging is, as with so many other bodies of knowledge, the story of old-fashioned research inflated to surreal proportions by the internet’s bellows. Yes, you can be a professional conlanger, but the competition is stiff.

Once upon a time, in the first half of the last century, J.R.R. Tolkien invented not just a single language, but a whole family of languages which he fully fleshed out in private and then had some of his characters speak. For example, Sindarin and Quenya, two forms of Elvish spoken by different communities in his Middle-earth novels, are not only descended from a common ancestor, but are related to a whole slew of other languages. (The actual inscription on the ring from The Lord of the Rings is in Sauron’s own conlang, Black Speech, but using the Elvish lettering system Tengwar, in case you were wondering.) In 1931, Tolkien gave a lecture called “A Secret Vice” about language invention. I recommend elvish.org as a further resource for the curious reader. As the century wore on, a few people repeated the trick: Linguist Marc Okrand filled out the vocabulary of Klingon for Star Trek III: The Search for Spock, and British novelist Alan Garner gave the Skeksis, the villains of Jim Henson’s The Dark Crystal, their own language.

What do I want to say with this new language that I can’t say in my native language—or any other language that currently exists?

On July 29, 1991, the first message was sent to the Conlang Listserv. According to FrathWiki, a hub of information about conlangs and their surrounding cultures, “the list evolved from some informal email conversations among an early group of language enthusiasts.” Originally housed at Boston University, then at the Datalogisk Institut in Denmark, then at Brown University, the Listserv flourished. Of course, it was quickly splintered by tempers. Due to the “constant bickering” between advocates of different auxiliary languages (Esperanto and its sisters), certain members were banished to their own Auxlang Listserv in 1996. Nobody is allowed to advocate for a language on Conlang.