What does a dying language look like? When parents stop speaking an ancestral language to their children, two main things happen. First, the grammar gets simplified, in the manner of a creole (not necessarily a bad thing). Second, the “lexicon becomes impoverished” — basically, people forget words for things.

It’s what happened to my English when I went to China to visit family in the fourth grade. I did speak English there, but not a lot of it, and with people who knew only to speak about simple subjects. On the drive back from the airport in the U.S., I remember seeing an ambulance and being alarmed that my brain had no word to describe this sight.

“Ambulance!” my Dad said, laughing. Ambulance? “Ambulance, ambulance, ambulance…” I repeated to myself, aloud. It sounded kind of ridiculous. But as I re-acculturated to being surrounded by English all the time, the reverse started to happen. Piece by piece, I forgot Chinese words not relevant to my daily life here, so that when I speak it today, I sound like a small child, struggling for words.

This struggle, in my view, is the main hurdle to speaking multiple languages. School teaches us to obsess over grammar rules, but even if you know all the rules, you still won’t be able to express yourself without vocabulary. Relating to this idea, some in the language learning community argue that language “fluency” depends on context. In one language, you may be “fluent” in talking about house matters; in another, you are fluent when talking about international politics.

I think that’s bullshit, and here’s why. I don’t know how to talk comfortably about auto mechanics in any language, but I am fluent in English. In English I would be able to point at an engine and say something like, “this circular gear that connects to the axle is rattling dangerously”, despite not knowing the specialist vocabulary. I cannot comfortably do the same thing in Chinese, so I would not say that I am fluent in that language.

Esperanto, as a ridiculously productive language, challenges this fluency paradigm. The see-through structure of its vocabulary, where words fit together like Lego blocks that you can individually see, enables new speakers to quickly plug gaps in their vocabulary by inventing new words, but in a way that is reliably understood by anyone who understands Esperanto grammar.

Take the adjectival form (varma) of the word for “heat” (varmo), which means “warm”. Add the “greater” suffix (varmega) to get the word for “hot”, or the “lesser” suffix (varmeta) to mean “lukewarm”. Literally translating these forms into English would result in circumlocutions like “a bit warm” or “more than warm” — but those phrases don’t quite capture the meaning, and literally translating them back into Esperanto would result in something else.

It’s hard to make analogies of the extremely pervasive system in Esperanto to English, because the creative use of suffixes in English is not normal. The few productive suffixes we have, like “-ette” or “-esque”, stigmatize any word with the connotation of snobbery, by their visible connection to French. If we think using this analogy, Esperanto’s derivation system seems trivial and foreign, rather than essential and powerful.

Instead, I want you to think back — “Only ’90s kids will get this!”— to the Final Fantasy series of role-playing video games, and to other JRPGs who followed the same formula. (They’re still around, but gaming is far rarer for adults.) When you first learn a spell, like “fire”, it produces a weak result. But then you practice it, and you can cast the second level of “fire” as “fira”. The third level of fire is “firaga” and the most destructive, “firaja”.

It seemed a bit foreign, but the idea was easy to pick up. When “thunder” upgraded to “thundara” we could predict that the next level was “thundaga”, and so forth. After having played the game for a while, if you saw someone cast the spell “curaja”, you would automatically know that it was a fourth-level spell of something, even if you didn’t know that “cura” is the second level of the “cure” spell.

Esperanto’s whole system of word-building is like this (I haven’t even gone into when you combine two or more root words, where the fun really starts), except that Esperanto is totally consistent. I cannot overstate the helpfulness of this property, and its responsibility for the amazing speed at which people can learn and readily use Esperanto. It is a blessing that only planned languages can have.

Why does total consistency matter? Take English, which like all natural languages has irregularities in its grammar. Unless you are a seriously studied etymologist, the only way that you would know that “geese” is the plural of “goose” is if you saw both forms in context, and committed both words separately to memory. Even though English is mostly regular, you cannot always trust that a word which ends in “s” is plural, nor that English words ending in other letters (“-i”, “-a”…) are not plural.

Although people who have memorized many, many words can make educated guesses and post-hoc rationalizations, there are so many cases in which you cannot instantly “figure out”why something is said a certain way in English, in the way that you can immediately intuit that “varmeta” is the diminutive of “varma” (before you learn what “varma” means!) in Esperanto. Correctly having the confidence that the rules which you memorized will always work, greatly helps with fluency.

I have been playing with Esperanto for less than a week, and I am already able to read (with heavy dictionary help) articles about subjects that actually interest me. Not children’s books or made-up stories, but articles on subjects like Neutral Moresnet and internet technology. Perhaps more importantly, these texts are written not just by an exclusive cabal of native- and near-native speakers who have dedicated years to study of an irregular language, before they feel confident enough to publish their thoughts.

In this way, Esperanto is as democratizing and empowering as it is international. It also makes self-expression easier, more forgiving on our memory, and even more creative. The old, powerful idea that only the few entrenched colonial languages could express advanced thought has long been debunked. Only the forces of historical and cultural inertia, and not efficiency or choice, tie us to the natural languages that we speak. Why choose to be a muggle?