Why 500? Why not all of them? For one thing, no one knows how many there are. Any claim to completeness in a list would surely be undone by the discovery of yet another self- published book or pamphlet in a library storage room somewhere. Another problem is determining what should count as an invented language. Should a few lines of made-up gibberish in a novel earn a place on the list? What about a sketch of an idea with none of the detail filled in?

When I started assembling this list, I had the ambitious intention to be as complete as possible, to include every project that anyone anywhere had any evidence for, but this soon proved impractical. The story I was trying to tell got lost in a swamp of data. I wanted the list to be big enough to impress, to make you exclaim, “I had no idea there were so many!” But I also wanted it be manageable enough to serve as a sort of mini-history, where just by looking at the dates and the names of the languages you could spot some general trends and get a sense of the connections between the ideas and the times.

I culled my list from the more than 900 languages covered in Alexander Dulichenko’s Mezhdunarodnye vspomogatel'nye jazyki (“International auxiliary languages,” 1990). This massive piece of research includes all of the projects covered by previous overviews, such as the Histoire de la langue universelle of Louis Couturat & Leopold Leau (1903), the Bibliografio de internacia lingvo of Petr Stojan (1929), the Historio de la mondolingvo of Ernst Drezen (1931), and the Précis d'interlinguistique générale et spéciale of Marcel Monnerot-Dumaine (1960) in addition to others mentioned in various sources. Dulichenko’s work is about as complete as you can get. It’s in Russian, and it’s not easy to get ahold of, but you can find it at some major universities and the Library of Congress.

In deciding what to include in my own list, I didn’t set any strict criteria. I just used my judgment and aimed for a list that would tell the story without distorting the facts. I left out a lot of works titled Pasigraphie, but put in enough to show that pasigraphies (universal writing systems) were big in the early 19th century, and still popped up occasionally after that. Although many languages from the early 20th century got left out on account of having boring names (how many variations on “Lingua International” do you need to get the picture?), there are enough in there, proportionally, to highlight the explosion in the number of projects during this era. Languages with strange or interesting names got in, as did those whose authors exposed their desire for personal glory by naming their projects after themselves (see, for example, Isly’s Linguum Islianum (1901), Ostaszewski’s Ost (1926), Anderson’s Ande (1960). I left out quite a few projects that were just reforms or improvements of other projects, but put in enough to show how widespread the “reform and improve” disease is among language inventors.

I included any work that I had seen myself in a library but had not seen in anyone else’s list of invented languages (e.g., the Universal Language of James Ruggles (1829), Walter Cuthbertson’s Standard World Language (1919)). I avoided works that involved too much uncertainty about dating or authorship – unless there was something intriguing about it (who was this Prince Immanuel of Jerusalem, the creator of Universal (1914?)?) Languages with weird names got in, as did languages from underrepresented countries such as Ghana (El-Afrihili, 1970), India (Koine Romai, 1973; Om, 1925; Sputnik, 1964), Iran (City-language, 1959), Nigeria (Guosa, 1981), Vietnam (Frater, 1957).

If an inventor had multiple languages, I sometimes admitted only one — Weferling’s Intal (1956) made it in, but not his Intal II (1964) or III (1968) — but for especially prolific inventors, I might include the whole bunch. (Hats off to Petr Stojan, who gave us, over the years from 1911 to 1926, Spriranta, Aryana, Ariana, Amiana, Liana, Unita, Espo and Eo.) 

Dulichenko’s list only goes as far as 1973. Past 1973, I simply included languages I had heard of, or seen myself in libraries. The criteria for dating a language require some explanation. Generally, the year given for a project represents the initial date of publication in an article or a book. I date Tolkien’s languages, for example, as 1955, despite the fact that he had already been working on them for 40 years by that point, because that is when he first published information about them (in the appendix to the third book of The Lord of the Rings). 

The dating of languages in the Internet age gets even more complicated. The years given for most of the languages I list from 1990 on represent (approximately) the first posting about the language on the web, in a newsgroup, or on a site dedicated to the language. The “conlangs” or “artlangs” I have listed here amount to a vanishingly tiny portion of the number that are out there. Sites like langmaker.com list hundreds of them. On forums like the “zompist” bulletin board (www.spinnoff.com/zbb), new languages are born every day. I have only listed the projects that I mention in the text, along with a few other especially noteworthy or well-developed ones – languages that most of the highly regarded conlangers will have heard of.