Esperanto Subordinate Clauses: ke, kiu, kiam and Where the Commas Go

A subordinate clause is a whole sentence stuffed inside another sentence. English does it constantly and casually, and it does it with a lot of quiet shortcuts: dropped conjunctions, stranded prepositions, tenses that lie about when things happen. Esperanto does none of that. It builds the same sentences, but everything is said out loud.

That makes this a short article with a high payoff. There are four rules and one punctuation habit.

ke, and why you cannot drop it

Ke is that as a conjunction. It introduces a complete statement and plays no part inside it.

Mi scias, ke vi venos. - I know that you will come.

Ŝi diris, ke la libro estas bona. - She said the book was good.

English will happily lose that that: I know you're coming. Esperanto will not, ever. Mi scias vi venos is not a sentence.

There is a reason, and it is the same reason the accusative exists. Esperanto word order is free, so position tells you nothing. Without ke, nothing in mi scias vi venos marks where the inner clause begins. The conjunction is the boundary marker, and boundary markers do not get to be optional.

ke plus -u: the bit English does with an infinitive

After a verb of wanting, asking, ordering or permitting, the inner verb takes -u, the volitive ending from the verb tenses article.

Mi volas, ke vi venu. - I want you to come.

Li petis, ke ni helpu. - He asked us to help.

Ŝi diris al mi, ke mi atendu. - She told me to wait.

Look at the English on the right of those. Every one of them uses an infinitive with its own subject attached (you to come, us to help). Esperanto has no such construction. Mi volas vin veni is not a thing. When the wanted action has a different subject from the wanting, you need ke and you need -u.

The same applies to purpose. Por ke vi komprenu - so that you understand. Por on its own plus an infinitive works when the subject is the same (mi venis por helpi, I came to help), and por ke plus -u takes over when it changes.

ĉu, not se

For a yes-or-no question inside a sentence, English uses whether or if, and the if is a trap.

Mi ne scias, ĉu li venos. - I do not know whether he will come.

Ŝi demandis, ĉu ni havas monon. - She asked whether we had any money.

Se means if in the conditional sense only - se li venos, mi estos feliĉa, if he comes, I will be happy. It cannot introduce an indirect question, and mixing the two is the single most common English-speaker error in this area.

Other indirect questions just keep their question word, with no inversion and no extra machinery, because Esperanto has no inversion to begin with: Mi ne scias, kie li loĝas. Mi demandis, kiam ŝi venos.

Relative clauses: kiu, kio, kies

Kiu stands in for a noun and does a job inside its own clause. This is where the real work is, so here is the whole thing in one table. The noun la viro is the subject of the main sentence throughout, and it makes no difference at all to kiu:

That last row is the one to memorise. The -j comes from outside, the -n comes from inside. The relative pronoun agrees in number with the noun it points back at, but takes its case from the job it does in its own clause. Two endings, two different sources, and no other rule to learn.

Prepositions go in front, never at the end: la domo, en kiu mi loĝas, the house I live in. English strands them; Esperanto has nowhere to strand them to. And the direction rule from the accusative article still applies, so la ĉambro, en kiun li iris is the room he went into.

Kiu also works as a determiner in front of a noun: Mi ne scias, kiun libron li legas - I do not know which book he is reading.

Kio is the other one, and the split is clean. Use kio when there is no noun to point at:

Mi ne komprenas tion, kio okazis. - I do not understand what happened. (after tio)

Ĉio, kion li diris, estis vera. - Everything he said was true. (after ĉio)

Li venis malfrue, kio ĝenis min. - He arrived late, which annoyed me. (pointing at the whole clause)

That third one matters. English uses which for both a noun antecedent and a whole-clause antecedent, and Esperanto splits them: kiu for the noun, kio for the clause. Getting this right is one of the quickest ways to stop sounding like a translated Englishman.

While you are here, note the pair tio, kio against tio, ke. Mi ne komprenas tion, kio okazis is what happened. Mi ne komprenas tion, ke li foriris is the fact that he left. The correlatives article sets out the whole ti- / ki- grid; this is that grid doing its day job.

kiam, and telling the truth about tense

Time clauses use kiam, and they use the tense that is actually true.

Kiam mi venis, li dormis. - When I came, he was sleeping.

Kiam li venos, mi diros al li. - When he comes, I will tell him.

Read that second one again. English says when he comes, present tense, about something that has not happened. Esperanto says kiam li venos, future, because it is in the future. Every verb carries its real time, everywhere, and there is no sequence-of-tenses rule shifting things backwards to agree with the main verb.

The same principle explains a sentence that looks wrong to English eyes:

Li diris, ke li estas malsana. - He said he was ill.

Estas is present because he was ill at the moment he spoke. If you write li diris, ke li estis malsana, you have said something different: he said he had been ill. English collapses those two; Esperanto keeps them apart, for free.

The rest of the time vocabulary follows the same pattern: dum (while), ĝis (until), post kiam (after), tuj kiam (as soon as), and antaŭ ol (before), which takes an infinitive when the subject is unchanged (antaŭ ol foriri) and a full clause when it changes (antaŭ ol li foriris).

The commas

Esperanto punctuates subordinate clauses generously, and the convention is simple enough to state in three lines:

• A comma goes before every subordinate clause: before ke, ĉu, se, ĉar, kvankam, and before every ki- word starting a clause.
• If the clause sits in the middle of the sentence, it gets a comma at both ends: La viro, kiu venis, estas mia frato.
• If it comes first, the comma goes after it: Kiam li venis, ni manĝis.

English has a rule about restrictive and non-restrictive clauses here - the man who came against my brother, who came - and marks the difference with commas. Esperanto has no such rule. It commas both, and if the distinction matters you make it with words rather than punctuation.

Some contemporary writers punctuate lightly in the English style and leave out the comma before ke. I would not. The comma before ke is Zamenhof's own practice and remains the majority one, and in a language with free word order it is doing genuine work: it tells the reader, before they have parsed anything, that a new clause has started.

What to take away

• Ke is never dropped.
• After wanting, asking or purpose, the inner verb takes -u: mi volas, ke vi venu.
• Indirect yes-or-no questions take ĉu, never se.
• Kiu gets -j from its antecedent and -n from its own clause. Kies never changes.
• Kio for a whole clause or after tio, ĉio, io, nenio.
• Time clauses use the real tense: kiam li venos.
• Comma before every subordinate clause, and after it too when it is in the middle.