Ido is a constructed language, designed to be an international auxiliary language, which was created in 1907. It was derived from Esp­e­r­an­to1 by a largely-French cohort of Esperantists (particularly Louis de Beaufront), intended to address perceived flaws in that language.

There is a certain amount of bitterness from old school Esperantists towards Ido and its (few remaining) speakers. This piece(external link) (extremely inaccurate where it describes Ido’s linguistic features) is fairly typical. When Ido was first put forward in 1907, not only were its suggested improvements contentious but there was controversy over violations of due process at some kind of international language convention or whatever (basically there was a rule that the inventor of a language couldn’t defend their own language at the convention, and de Beaufront pretended not to be the inventor of Ido so he could defend it personally), and it caused a big schism in the Esperantist movement. Those who stuck with Esp­e­r­an­to (the majority) pointed to the example of Ido as proof that they should never reform their language and must “stay pure” lest they degenerate into in-fighting. Meanwhile, Idists (the minority) bickered about what further reforms, if any, they should make. This, unfortunately, limited its appeal to prospective learners, as they seemed to be faced with an ever-shifting target.

Ido suffered a huge loss of momentum when one of its leading proponents, Louis Couturat, died in a car crash in 1914. Shortly after that, of course, the First World War broke out, and internationalism in general went out of vogue for a while, replaced by a nationalist war frenzy. New conlangs like Occidental and Novial (the latter of which being the brainchild of one of Ido’s own co-creators, Otto Jespersen) siphoned away large fractions of its speakerbase. The Idist movement was fairly residual (but never fully dormant) after the 1920s, although with the rise of the Internet it’s gained a new lease on life. It seems like today it vies with Interlingua for the status of third-most spoken IAL in the world.



Ido was designed to have a more logical and symmetrical pronoun system than natural languages (and than Esp­e­r­an­to). Ido’s primary six personal pronouns are:


* Tu is informal, vu is formal. Originally it was intended that vu would be used in most circumstances, with tu reserved only for family and close friends. However, modern-day Idists use tu pretty liberally.

While Ido totally allows you to use the genderless pronoun lu for anyone or anything you want, you can also optionally specify gender in your third-person pronouns. This subsidiary set of pronouns goes:

masculineil, iluili
feminineel, elueli
neuterol, oluoli

The forms with -u and the forms without are totally interchangeable, depending on what you think sounds better (it’s not a subject-object dis­tin­c­tion, for example). I’m not sure why Ido’s creators decided to include this kind of optional variation (they did it in a few other ultra-common words too) but they did.

There are also three other pronouns (excluding relative pronouns):

  • on, onu: a generic pronoun, like “one” in English or (less formally) “generic you” or “generic they”.
  • su: a third-person reflexive pronoun. Where this is really handy is possessive adjectives, because it lets you distinguish between e.g. “she’s carrying her (own) bag” and “she’s carrying her (i.e. a different person’s) bag”.
  • lo: used to substitute not for a single noun but a whole phrase or concept, like Ni parolis pri lo “We were talking about that” or Me ne facis lo! “I didn’t do it!”. It can also be used with an adjective, like lo in Spanish, to mean something like “that which is” (e.g. lo bona “the good, that which is good”).


Unlike many natural languages as well as Esp­e­r­an­to, unmarked forms of nouns are strictly gender-neutral, with exactly four exceptions:

  • matro: mother
  • patro: father
  • muliero: woman
  • viro: man

(There are also genitoro and adulto, as gender-neutral words for “parent” and “adult”, respectively.) For all other words, the unmarked form implies nothing about a person’s (or animal’s) gender and you have to add a suffix if you want to specify. Some examples:

  • spozo (spouse) – spozino (wife) – spozulo (husband)
  • amiko (friend) – amikino (female friend) – amikulo (male friend)
  • hano (chicken) – hanino (hen) – hanulo (rooster)

To be fair, some old-timey self-teaching resources (like “Ido For All”, ahem) may not reflect this because of old school social norms… like the aforementioned “Ido For All” insists on translating policisti as “policemen”, when it’s actually “police officers”. However, the actual grammar of Ido is very clear on the matter.

Phonology and Orthography

Ido uses all 26 standard letters of the Latin alphabet, with no diacritics. It employs three digraphs:

  • “ch” for [tʃ]
  • “sh” for [ʃ]
  • “qu” for [kw]

…and otherwise letters have a single consistent sound, and sounds have a consistent single representation. Most of these sound-letter correspondences are the same as in Esp­e­r­an­to, except that Ido “j” represents [ʒ] and “y” represents [j]. Ido also, of course, uses some letters that don’t exist in Esp­e­r­an­to, like “w” (for [w]) and “x” (for [ks]).

Ido doesn’t allow as many difficult consonant clusters as Esp­e­r­an­to. For example, kv- was replaced with qu-, and kn- and sc- are gone entirely. Some Esperantists criticise Ido for this, because they perceive it as Anglo-French-centrism. Idists, though, feel that the simplified consonant clusters are more accessible cross-linguistically, not just for English and French speakers. That said, proponents of newer conlangs like Pandunia would criticise Ido for still retaining clusters from Esp­e­r­an­to that are comparatively uncommon and difficult for speakers of many non-European languages, like str-.


Ido has more word roots than Esp­e­r­an­to. There are about three major reasons why Ido coined more roots:

  • Wanting more sound distinction between words that fill the same semantic role (like directions or pronouns) but have very different meanings. Esp­e­r­an­to, for example, has word pairs like dekstra “right” and maldekstra “left” – if you miss the first syllable in a noisy environment, that could lead to a big misunderstanding. Similarly, mi “I/me” and ni “we/us” sound super similar, which is why Ido changed the first one to me.
  • Believing that Esp­e­r­an­to went way too far using the suffix mal- “un-” everywhere. Esp­e­r­an­to also has word pairs like bona “good”/malbona “ungood” (or “bad”), fermi “to close”/malfermi “to unclose” (or “open”) and luma “light”/malluma “unlight” (“dark”). For really really basic words like this, Ido’s creators were like, c’mon, just give them their own words.
  • Not liking the more idiomatic or euphemistic combination of word roots + affixes to create new words that had meanings beyond the strict combination of root + affix. For example, lernejo (lit. “learning place”) meaning “school” specifically.

Some Esperantists think that Ido ditched Esp­e­r­an­to’s entire affix system and became all “word roots” that have to be learned individually, for some reason. This is not true. In fact, Ido has more distinct affixes than Esp­e­r­an­to does (see next section). I feel like Ido just has a greater number of words (roots and derivations combined), each of which is used more precisely with a more limited meaning than in Esp­e­r­an­to.

Strictly speaking, Ido draws its vocabulary from the same six source languages as Esp­e­r­an­to: English, French, Spanish, Italian, German and Russian. There is a perception that Ido discarded many of Esp­e­r­an­to’s Germanic and Slavic word roots for Romance and English ones, although this really overestimates how much of Esp­e­r­an­to was Germanic or Slavic in the first place (a 1987 study found 84% of Esp­e­r­an­to’s vocab was Romance, 14% Germanic, and only 2% Slavic or Greek put together – although I’m not sure how the study accounted for words shared across more than one language family). Like Esp­e­r­an­to, in theory, Ido tried to find the word root that was most universal across its source languages. Indeed, a lot of the word changes Ido made from Esp­e­r­an­to were from one Latinate/Romance word to another, like replacing Latinate scii with modern Romance savar, or Italian/French-ish fari with Portuguese-ish facar, or Italian/French meti to Catalan/probably other languages’ pozar.

Of Ido’s word roots, it’s estimated that:

  • 91% are found in French
  • 83% are found in Italian
  • 79% are found in Spanish
  • 79% are found in English
  • 61% are found in German
  • 52% are found in Russian

Of course, the shared root isn’t always in the same form. e.g. Ido domo “house” has nothing in common with English house, French maison or Spanish casa. But these languages do all have an adjective domestic/domestique/doméstico, in which this word root does appear, and so it’s said that this root is found in those languages.

Word Derivation

Like Esp­e­r­an­to, Ido derives a lot of words by combining a word root with affixes (and, for most word classes, a final suffix to indicate what kind of word it is, whether a noun or an adjective or whatever). There are a few dozen affixes that are used, some more common than others.

Ido is very precise in how it uses its affixes, because it holds that affix use must be reversible. That is, you shouldn’t only be able to work out the meaning of a derived word from knowing the root + affixes, but you should also be able to work out the meaning of a root from knowing the derived word and “unapplying” the affixes. This is different from how Esp­e­r­an­to thinks of affixes! And it results in word differences between the languages. The classic example is that in Esp­e­r­an­to you can go from krono “crown” to kroni “to crown”. Ido instead requires kronizar (lit. “to furnish with a crown”). If kronar meant “to crown”, then working backwards to krono might give you “a coronation”, which would obviously be wrong.

Esp­e­r­an­to also has some idiomatic words where you’re just supposed to know that the meaning isn’t the literal meaning, like vortaro (lit. “a word collection”) means “dictionary” and lernejo (lit. “a learning place”) means specifically “school” and not any other place you could learn. Ido has different words for these – vortolibro (lit. “word-book”) for “dictionary” and a distinct root, skolo for “school”,2 while its cognates vortaro and lerneyo mean “vocabulary” and “classroom” (but could be a metaphorical classroom, like a digital learning space) instead. To me this feels more logical, and like a “purer” implementation of the “deriving words through roots and affixes” principle.

There are two classes of criticisms made about Ido’s approach to word roots and derivation. The first is that Ido is too complicated for making everything so much more exact. There are often multiple Ido translations for a single Esp­e­r­an­to affix, so an Esperantist has to decide which exact sense of the affix they mean in order to translate into Ido correctly, which some of them find annoying (but at least this is the group of Esperantist who gave it a shot, which is a start!).

Then the other complaint is that Ido has too many word roots, and has lost the agglutinative simplicity that made Esp­e­r­an­to so appealing in the first place (as I mentioned in the last section). Now to be fair, there are a number of word roots listed in various Ido dictionaries that I don’t think really need to be there. For example:

  • abreviar: you can just say kurtigar, with the same meaning (“shorten”).
  • ameliorar: you can say plubonigar (“improve” or “make better”).
  • dicionario: as an alternative to vortolibro (“dictionary”), which clearly you should just say instead.

That said, if I look up an English-to-Ido dictionary, the alternatives I suggested are listed as preferred. I haven’t really read enough Ido, at a high enough level, to see how Idists usually use their language. However, clearly it is possible to write Ido using these elegant derived words instead of the clumsy procomposed borrowings from French or wherever else.

Table of Correlatives

Where Esp­e­r­an­to’s table of correlatives is strictly regular, Ido’s includes a lot of irregularity, mainly to make the different interrogatives and demonstratives more distinct from one another and also for more similarity with Rom­ance languages or Latin. Ido’s system is certainly more arbitrary (especially for people with zero prior Latin/Romance exposure), but with the words being more dissimilar and therefore harder to mix up with each other, I feel like it’s ultimately more memorable. Here is Ido’s full table (more or less) of correlatives, as borrowed from Wikipedia(external link):

“What” “That” “Some” (ula) “Any” (irga) “No” (nula) “Every” (omna)
Individual (-u) qua ita ulu irgu nulu omnu
Thing (-o) quo ito ulo irgo nulo omno
Plural (-i) qui iti uli irgi nuli omni
Adjective (-a) qua ita ula irga nula omna
Motive (pro) pro quo pro to pro ulo pro irgo pro nulo pro omno
Place (loke) ube ibe ulaloke irgaloke nulaloke omnaloke
Time (tempe) kande lore ulatempe irgatempe nula­tempe sempre
Quality (-a) quala tala ulaspeca irgaspeca nulaspeca omnaspeca
Manner (-e) quale tale ule irge nule omne
Quantity, adj. (-a) quanta tanta kelka irgaquanta nulaquanta omnaquanta
Quantity, n. (-o) quanto tanto kelko irga quanto nula quanto la tota quanto


So you want to learn more about Ido? Well, here are the webpages and sites that I’ve found most useful:

  1. Well, strictly speaking it’s derived from the 1894 proposal for Reformed Esp­e­r­an­to, which was rejected by the majority of Esperantists and therefore not the form of Esp­e­r­an­to used today. ↩︎

  2. Esp­e­r­an­to also has “skolo” actually but only for like “a school of thought” ↩︎

Did you know? I’ve posted other content tagged ‘Ido’! If you want to see what else I’ve written on this topic, you can do so here.