Questions in Esperanto: Ĉu, the Ki- Words and How to Answer

English makes you pay for every question. To ask do you speak Esperanto? you conjure an auxiliary verb from nowhere, invert it with the subject, and demote the main verb to its bare form - three operations, none of which mean anything, all of which are compulsory. French offers you a choice of three mechanisms with three registers. German inverts. Mandarin bolts a particle onto the end.

Esperanto does this:

Vi parolas Esperanton. - You speak Esperanto.

Ĉu vi parolas Esperanton? - Do you speak Esperanto?

One word, ĉu, at the front. The statement underneath is untouched.

Ĉu: the question mark you say out loud

Ĉu has no translation because it has no meaning. It is a pure interrogative flag: whatever statement follows it is being asked rather than asserted. That makes it the entire yes/no question system, in every tense, for every verb, with no exceptions to memorise:

Ĉu ŝi venos? - Will she come?

Ĉu la kafo estas varma? - Is the coffee warm?

Ĉu vi iam estis en Parizo? - Have you ever been to Paris?

For English speakers this is a small liberation. All that machinery - do-support, inversion, the ban on inverting main verbs but not auxiliaries - simply is not there. You build the sentence you would have said anyway and put ĉu in front of it. Zamenhof borrowed the word from Polish czy, which does the same job, and it is one of the best imports in the language.

The discipline to build: resist the urge to invert. Parolas vi Esperanton? is what English instinct produces, and it is wrong - not stylistically wrong, structurally wrong. The word order of the statement survives into the question, always.

The ki- words: questions with content

When you want more than a yes or a no, Esperanto hands you the ki- column of the correlatives table: kiu (who, which), kio (what), kia (what kind of), kie (where), kiam (when), kial (why), kiel (how), kiom (how much), kies (whose). The full table, with its beautiful nine-by-five regularity, lives in the correlatives article; this page only needs the ki- row and what to do with it.

What you do with it: front the ki- word, and leave the rest of the sentence declarative.

Kie vi loĝas? - Where do you live?

Kial vi ne venis? - Why did you not come?

Kiom da kafo vi volas? - How much coffee do you want?

Again no inversion: kie vi loĝas?, not kie loĝas vi? (grammatical, but marked - it fronts the verb for emphasis, which is a stylistic choice, not question formation).

Two mechanical points. First, ki- words take the ordinary endings, because they are ordinary words: kiun vi vidis? (whom did you see? - kiu is the object, so it wears the accusative -n), kiuj venos? (which ones will come? - plural). Forgetting the -n on kiun is the commonest slip in the whole topic.

Second, ĉu and a ki- word never share a direct question. A ki- word IS the question; adding ĉu is asking twice. If you catch yourself writing ĉu kiam..., one of the two has to go.

Answering: jes, ne, and the trap

Positive questions behave themselves. Ĉu vi venos? - jes (yes) or ne (no), exactly as English leads you to expect.

Negative questions are where an international language earns its keep, because the world's languages genuinely disagree about what yes means in reply to one:

Ĉu vi ne venos? - Are you not coming?

Esperanto's convention: jes affirms the fact, not the phrasing. Jes means I AM coming; ne means I am not. You answer the underlying state of the world and ignore the question's negative wrapping - the same convention as English, so anglophones can coast.

But a large part of the Esperanto world cannot. Japanese, among other languages, runs the opposite system: agreeing with a negative question means confirming the negative - yes (you are right), I am not coming. Learners import their home convention wholesale, in both directions, and a one-syllable answer to a negative question is therefore a coin toss in real international conversation. The negation article covers this same trap from the ne side; between the two pages the advice is identical: answer with a clause, not a syllable.

Ĉu vi ne venos? - Jes, mi venos! / Ne, mi ne venos.

Two extra words. Zero missed dinners.

Ĉu ne? - one tag to rule them all

English tag questions are a conjugation exercise in disguise: isn't it, doesn't she, won't they, haven't we, mustn't he - the tag reprocesses the whole sentence's auxiliary, polarity and subject. Esperanto replaces the entire system with one invariant tag:

Vi venos, ĉu ne? - You are coming, aren't you?

Estas bela tago, ĉu ne? - It is a lovely day, isn't it?

Ĉu ne? literally asks "is it not so?", and it never changes form. There is also a lighter version, bare ĉu?, which assumes less: vi venos, ĉu? is closer to you're coming, are you? - a genuine enquiry rather than a bid for agreement. Use ĉu ne? when you expect a nod, ĉu? when you actually want to know.

Indirect questions: ĉu as whether

Ĉu has a second job. When a yes/no question is folded inside another sentence, ĉu becomes whether:

Mi ne scias, ĉu ŝi venos. - I do not know whether she will come.

Li demandis, ĉu la kafo estas preta. - He asked whether the coffee was ready.

The trap here is English's fault: English uses if for both this and conditions, so anglophones write mi ne scias, se ŝi venos - and that is simply broken, because Esperanto's se is strictly conditional (se ŝi venos, mi ĝojos - IF she comes, I will be glad). The test is mechanical: if the English sentence still works with whether, the Esperanto wants ĉu. If only if works, it wants se.

Indirect ki- questions need no such care - the ki- word simply carries over: mi ne scias, kie li estas (I do not know where he is), diru al mi, kial vi ploras (tell me why you are crying). More on how these clauses attach in subordinate clauses.

What to take away

• Yes/no questions: ĉu + the unaltered statement. No inversion, no do-support, ever.
• Content questions: front a ki- word (kiu, kio, kie, kiam, kial, kiel, kiom, kies, kia); the rest stays declarative. Ki- words take -n and -j like any other word.
• Never ĉu and a ki- word in the same direct question.
• Negative questions: jes affirms the fact (jes = I AM coming). Conventions differ across the movement, so answer with a full clause.
• The universal tag is , ĉu ne? - and the more open , ĉu? when you are asking, not assuming.
• Indirect yes/no questions use ĉu for whether. Never se.

See also

• Correlatives - the full table the ki- words come from, and the other four rows that answer them.
• Negation - the other half of the negative-question trap, plus where ne goes and why it matters.
• The article la - chapter 12's companion piece on the other tiny word learners agonise over.
• Subordinate clauses - how indirect questions and ke-clauses attach to the main sentence.
• Word order and style - why kie loĝas vi? is emphasis, not question formation.