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Why is Kio never plural – Esperanto Correlatives Posted by on Aug 27, 2018 in Esperanto Language

Esperanto is an “Easy Language”

One thing which we all learn (hopefully) early on in our pursuit of Esperanto is that there’s no such thing as an “easy language.” While Esperanto speakers often report a higher level of success with Esperanto compared to other languages they’ve learned (or tried to learn), Esperanto is not without challenges. Top on that list are the accusative ending (-n), transitivity of verbs, and the “dreaded Table of Correlatives.”

This month’s topic, suggested by Sandio, focuses on one small aspect of the Correlatives. Sandio was a student at NASK this summer who helped me see this question in a new light.

Why is Kio always singular?

Why is "Kio" never plural? Photo courtesy Esperanto Variety Show

Why is “Kio” never plural? Photo courtesy Esperanto Variety Show

When I teach the correlatives, I usually start with the questions, but it applies equally well to the answers. Why are kio (what), tio (that), io (something), ĉio (everything), and nenio (nothing) always singular? Many of the correlatives are unchanging (kiel, nenies, and iam, for example) but the following question words can take grammatical endings like -j and -n. (Again, this applies to the answers too.)

  • kia -j, -n
  • kie -n
  • kio -n
  • kiu -j, -n

Note that these happen to be the correlatives that end in vowels. It’s easy enough to see why kie can’t be plural (it’s like an adverb) and if you understand the motion rule explained in Keys to understanding Esperanto prepositions, the same rule applies to adverbs, hence the -n. If you take kie off the list, it might seem surprising that kio, which asks about nouns, can’t be plural like nouns can be. This contrasts with  kiu and kia.

Sandio wanted to know why.

My usual answer is that kio is asking about something unknown. If it’s unknown, how can you know whether it’s plural or singular? Therefore, in Esperanto, we treat it as singular. At this point, a learner might say something like “What if I hold up a bowl of lumpy objects and ask ‘what are these?’ – that certainly sounds plural to me, even if I don’t know what they are.”

At that point, I usually punt. “The reason it can’t be plural is … just ‘cos.”

This wasn’t good enough for Sandio, who pressed the question. I did my best and moved on for the day onto other topics.

Inspiration hit the next day

As I mention briefly in this video, it struck me that we really do the same thing in English. When we don’t say “these” (which is really short for “these things” (tiuj aferoj)), “what” is basically always singular in English. Plural, in English, is reflected in the verb.

If I were to hold up a bowl of lumpy objects and ask about the contents of the bowl, I would ask:

  • What is in the bowl?

The same thing applies no matter what we’re talking about. I could ask “what is on the table?” and even if I was expecting a list of seven items (that is, even if I knew the answer was plural), I would never ask “what are on the table?”. As soon as we specify “what things are on the table”, we’re no longer talking about kio. (That would have to be kiuj aferoj estas sur la tablo?)

When we specify “these (things)”, we do use a plural verb in English:

  • Kio estas tiuj (aferoj)?
  • What are these (things)?

… that’s because “these things” is the subject. (These things are what?) It’s the same in Esperanto.

And it applies to “the answers.”

One thing I didn’t mention in the class at NASK is that not only applies equally well to the answers, but might be easier to see if we look at the answers first.

  • tio (that)
  • io (something)
  • ĉio (everything)
  • nenio (nothing)

We never say “that are”, or “something are”,  or “everything are” or “nothing are” – so why would we try to make tioioĉio, and nenio plural? The same thing applies to kio.

We learn by teaching

Someone asked me at the end of NASK what I learned while teaching. In the moment I couldn’t think of anything. (While NASK is an awesome experience, in many ways teaching there is just an extension of what I do every day all year long.) I wish I’d thought of this topic – because this certainly counts. Thanks, Sandio, for pressing your question and for suggesting that I write a blog post about it.

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About the Author:Tomaso

An Esperanto teacher since 1998, Tomaso (known in various corners of the online Esperanto world as "Salivanto") has been answering questions about Esperanto for almost two decades. He has been a regular contributor to Radio Verda, Esperanto Stack Exchange, Duolingo forums, and most recently his own YouTube Channel Esperanto Variety Show. Tomaso lives in upstate NY with four of the coolest Esperanto speakers in North America - his wife and kids.


  1. Richard A Stull:

    grande expliko…Rikardo

  2. Thomas:

    Mi malkonsentas. “Tiuj estas kioj?” estas frazo perferkte akceptelba.

    • Tomaso:

      @Thomas Just to be clear – “Thomas” above is not me (Tomaso.)

      You’re welcome to disagree, but you’re disagreeing with the Fundamento and 130 years of usage. PMEG calls kioj “netradicia kaj ankoraŭ nekutima.” As Liĉjo says elsewhere, it’s almost never used in writing and if it’s ever used, it’s used by people “pushing the limits” of the language.

  3. Robb Kvasnak:

    Mi uzas “kioj” – se ekz iu dirus al mi: en via lasta listo mankis kelakj aĵoj. Mi respondus: Ĉu, do kioj? Ankaŭ mi povus diri: Mi havas kelkajn librojn por vi. Ĉu vi volas scii kiojn?

    • Tomaso:

      @Robb Kvasnak Vidu ankaŭ mian respondon al “Thomas” supre.

      > You’re welcome to disagree, but you’re disagreeing with the Fundamento and 130 years of usage. PMEG calls this usage “netradicia kaj ankoraŭ nekutima.” As Liĉjo says elsewhere, it’s almost never used in writing and if it’s ever used, it’s used by people “pushing the limits” of the language.

      Here’s your dialog translated into standard Esperanto:

      Kvasnaka: Ĉu, do kioj?
      Normala: Ĉu, do kiuj?

      Kvasnaka: Ankaŭ mi povus diri:
      Normala: Krome, mi povus diri:

      Kvasnaka: Ĉu vi volas scii kiojn?
      Normala: Ĉu vi volas scii kiujn?

  4. Angelo:

    Dankegon! Mi havis la saman demandon, sed vi ĵus klarigis ĝin al mi. 😊

  5. Nekoninda:

    While no explanation is perfect, I find it useful to think of the -o correlatives as asking about or indicating categories. When I ask ‘Kio estas en la bovlo?’, I’m expecting an answer that names a category: Fruit, marbles, candy, eggs, etc. Even if there are multiple objects, I’m hoping to understand what single category they belong to. If I ask ‘Kio estas en la ĉambro?’, I expect an answer specifying a category like ‘libroj’, or even ‘homoj’. As Tomaso says, this is similar to English usage. When I ask this kind of question, I don’t expect an answer that identifies an individual, such as ‘The Fall of the Roman Empire’ or ‘George’.

    If I want to talk about individuals within a known category, then I use the -u correlatives. ‘Kiu libro estas sur la breto?’ is the question I’d pick when I want an answer like, ‘Harry Potter and The Philosopher’s Stone’. Or if I want to ask about an individual person, I would ask ‘Kiu estas la persono en tiu ĉambro de sekretoj?’ I’d be expecting an answer that specifies an individual, like ‘Harry Potter’, or perhaps ‘La Duon-Sanga Princo’. In general, we talk about categories of things with the -o correlatives, and about individuals within a known category using the -u correlatives.

  6. Liĉjo:

    The definitions of correlatives in -io are helpful. “Tio” = “kiu afero (aĵo, ideo, ks)”?

    “Kio” = “uzata por demandi pri afero, konkreta aŭ abstrakta”

    So the basic idea behind “io”, “kio”, “tio”, “ĉio”, etc. is an unspecified, unidentified, or unknown “thing”, singular.

    Usage of the -io correlatives in the plural is extremely rare, and tends to happen with people who are pushing the limits of the language, not with people who are learning Esperanto as it is actually spoken and written.

    I can ask “Kio estas tio, trans la strato?” if I see something and don’t know what it is. The answer might be “Ho, tio estas granda amaso de katidoj”.

    Once the thing is specified, the grammar changes.

    “Ho, katidoj! Ili estas ĉarmaj! De kie venis tiuj katidoj?”

    For people learning Esperanto, my advice would be not to use the io-correlatives in the plural. I don’t think I ever do.

  7. Liĉjo:

    If you approach Esperanto as a game or project of logic, you might come to the conclusion that words like “kioj” or “tioj” are normal parts of the language.

    But Esperanto isn’t a game or project. It’s a living language, with a living language community. And so what might be “logical” isn’t always “right”.

    How Esperanto is spoken today depends on at least 4 factors:

    1. The “Fundamento”, which established the basic grammar and structure of the language.

    2. Logic

    3. Practical decisions about how people use language

    4. 130+ years of actual usage by speakers.

    If you’re learning Esperanto, I’d encourage you to understand that forms like “kioj” and “tioj” are certainly not parts of normal Esperanto. When you’ve thoroughly learned the language, and start to interact with the Esperanto community, and the written literature, you’ll see just how infrequent that kind of usage is.

    There’s really no reason as a learner to spend time on marginal usages like this. If in the future you want to become an avant-garde author in Esperanto, you’ll be free to incorporate them in your work.

    • Tomaso:

      @Liĉjo The point of my blog post was to show that kio is singular not just because of 1, 3, and 4 (i.e. not “just ‘cos”), but also because of logic – and a logic which we naturally apply while speaking English. It seems my explanation helped some. If it doesn’t help others, I’m happy to fall back to “just ‘cos.”

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