A relative clause with kiu adds information about a person or thing already mentioned: la najbaro, kiu loĝas supre means “the neighbor who lives upstairs.” The clause both describes la najbaro and contains a pronoun—kiu—that represents that neighbor inside the added clause.
Esperanto uses the same four forms for people and things: kiu, kiuj, kiun, and kiujn. There is no separate choice corresponding to English who, which, and that. Number follows the word being described; case follows the relative pronoun’s job inside its own clause.
Building a kiu relative clause
Start with two sentences that mention the same referent:
Mi renkontis la novan najbaron. Li loĝas super ni.
I met the new neighbor. He lives above us.
Replace the repeated noun or pronoun in the second sentence with kiu, then attach that clause directly after the noun it describes:
Mi renkontis la novan najbaron, kiu loĝas super ni.
I met the new neighbor, who lives above us.
The main clause is Mi renkontis la novan najbaron. The finite relative clause is kiu loĝas super ni. Its verb loĝas has its own subject, kiu, which refers back to la novan najbaron.
The same pattern describes things:
Jen la ŝlosilo, kiu malfermas la malantaŭan pordon.
Here is the key that opens the back door.
Esperanto kiu makes no grammatical gender distinction. Context and the antecedent tell us whether it refers to a woman, a man, an animal, or an object.
Number: kiu or kiuj
Use singular kiu for one antecedent and plural kiuj for more than one:
La studento, kiu sidas apud la fenestro, venas el Brazilo.
The student who is sitting by the window comes from Brazil.
La studentoj, kiuj sidas apud la fenestro, venas el diversaj landoj.
The students who are sitting by the window come from different countries.
The plural ending belongs on the relative pronoun because it represents the plural antecedent la studentoj. It does not depend on the verb: Esperanto verbs never agree for person or number.
A coordination can also create a plural antecedent:
Nora kaj Leo, kiuj organizis la renkontiĝon, jam alvenis.
Nora and Leo, who organized the meeting, have already arrived.
English sometimes uses singular-looking who for any number. Esperanto visibly marks -j, so learners must keep track of the antecedent.
Subject and object forms
When the represented person or thing performs the relative-clause action, use kiu/kiuj:
Mi serĉas kuraciston, kiu parolas Esperanton.
I am looking for a doctor who speaks Esperanto.
When it receives the action, add accusative -n: kiun/kiujn.
Mi telefonis al la kuracisto, kiun vi rekomendis.
I phoned the doctor whom you recommended.
In the first sentence, the doctor speaks, so kiu is the subject. In the second, you recommended the doctor, so kiun is the object. The form of the antecedent in the main clause does not decide this. Compare la kuraciston, kiu parolas: kuraciston has -n because it is the object of serĉas, but kiu has no -n because it is the subject of parolas.
This independent case system is developed step by step on relative case inside the clause.
Put the clause next to its antecedent
A relative clause normally follows the expression it describes. Close placement prevents the listener from attaching it to the wrong noun:
Mi parolis kun la frato de Nora, kiu laboras en la biblioteko.
I spoke with Nora’s brother, who works in the library.
By default, kiu attaches to the nearest suitable noun, la frato. If Nora works at the library, reword the sentence:
Mi parolis kun Nora, kiu laboras en la biblioteko, kaj kun ŝia frato.
I spoke with Nora, who works in the library, and with her brother.
Free word order does not remove attachment ambiguity. Place the relative clause immediately after its antecedent or repeat a clear noun. This matters especially in long noun phrases containing de, where English can tolerate ambiguity that international Esperanto should avoid.
Identifying and additional information
Some relative clauses identify which referent is meant:
La gasto, kiu mendis teon, atendas la fakturon.
The guest who ordered tea is waiting for the bill.
The clause selects that guest from the relevant group. Other relative clauses add a comment about an already identified referent:
Amina, kiu mendis teon, sidas apud la fenestro.
Amina, who ordered tea, is sitting by the window.
The name Amina already identifies the person, so the relative clause adds information rather than selecting her.
Traditional Esperanto frequently writes a comma before kiu in both functions. PMEG notes that some writers omit commas around an identifying clause and that there is no absolute rule; a comma is always possible. For learners, consistently using a comma at the finite-clause boundary is a clear, internationally readable default. The finer discourse distinction is covered on nonrestrictive relative clauses.
Tiu, kiu and relative clauses without a noun
Kiu can describe the demonstrative tiu when no noun is expressed:
Tiu, kiu trovis mian monujon, bonvolu kontakti la akceptejon.
The person who found my wallet should please contact reception.
Plural tiuj, kiuj means “those who”:
Tiuj, kiuj jam pagis, ne bezonas denove registriĝi.
Those who have already paid do not need to register again.
In proverbs and compact general statements, tiu may be left understood: Kiu demandas, tiu lernas or simply a contextually supported Kiu demandas, lernas. The full tiu, kiu pattern is the clearer A2 choice. Do not confuse this relative kiu with interrogative kiu: no identity question is being asked; the clause describes a referent.
Do not omit the relative pronoun
English can say the book I bought, omitting that/which. Standard Esperanto cannot omit the relative kiun:
Jen la libro, kiun mi aĉetis hieraŭ.
Here is the book that I bought yesterday.
The pronoun is doing real grammatical work: it is the object of aĉetis and links the clause to la libro. Ke cannot replace it because ke only introduces content; it does not stand for an argument inside the relative clause.
Mi legis la mesaĝon, kiun vi sendis, sed mi ankoraŭ ne respondis.
I read the message you sent, but I have not replied yet.
This explicit linking is one reason Esperanto relative clauses remain clear despite flexible word order.
Tense and mood inside the relative clause
The relative clause is finite and chooses its own tense:
Mi revidos la kolegon, kiu helpis min hieraŭ.
I will see again the colleague who helped me yesterday.
Future revidos and past helpis refer to different times. A past main verb likewise does not force backshift:
Ŝi prezentis al mi la teknikiston, kiu riparos la aparaton morgaŭ.
She introduced me to the technician who would repair the device the next day.
Use -os because the repair is future from the relevant viewpoint. Conditional -us would make it hypothetical. Volitive forms can occur when the relative clause expresses a desired qualification:
Ni bezonas volontulon, kiu helpu ĉe la enirejo.
We need a volunteer who will help at the entrance.
Here helpu presents the help as the wanted role, not an established fact. In a factual description—la volontulo, kiu helpas—use real mode.
Questions, negation, and conversation
Ĉu vi konas iun, kiu povas ripari biciklon?
Do you know anyone who can repair a bicycle?
Mi ne trovis dosieron, kiu enhavas la finan tabelon.
I did not find a file that contains the final table.
The outer question or negation does not change the relative pronoun. Its form still depends on number and its internal clause role.
— Kiu estas Leo? — Li estas la kolego, kiu sidis apud mi dum la vespermanĝo.
— Who is Leo? — He is the colleague who sat next to me during dinner.
The first kiu is interrogative; the second is relative. The question asks for identity, while the answer’s relative clause describes the already mentioned colleague.
Common Mistakes
1. Replacing relative kiu with ke.
❌ La virino, ke laboras ĉi tie, estas mia onklino.
Incorrect — ke cannot stand as the subject of laboras.
✅ La virino, kiu laboras ĉi tie, estas mia onklino.
The woman who works here is my aunt.
2. Omitting the relative pronoun as English allows.
❌ Jen la foto, mi sendis al vi.
Incorrect — the relative object is missing.
✅ Jen la foto, kiun mi sendis al vi.
Here is the photo that I sent you.
3. Forgetting plural agreement.
❌ La najbaroj, kiu loĝas supre, havas katon.
Incorrect — kiu represents the plural antecedent najbaroj.
✅ La najbaroj, kiuj loĝas supre, havas katon.
The neighbors who live upstairs have a cat.
4. Copying the antecedent’s accusative onto a subject relative.
❌ Mi renkontis la flegistinon, kiun laboras nokte.
Incorrect — the nurse is the subject of laboras, so the relative form is kiu.
✅ Mi renkontis la flegistinon, kiu laboras nokte.
I met the nurse who works nights.
5. Backshifting a future relative clause.
❌ Ŝi montris al mi la ĉambron, kiu estus libera morgaŭ.
Wrong for a firm future fact; estus makes availability hypothetical.
✅ Ŝi montris al mi la ĉambron, kiu estos libera morgaŭ.
She showed me the room that would be free the next day.
Key Takeaways
- Relative kiu represents an earlier person or thing inside a finite describing clause.
- Use kiu/kiuj for number and -n only when the relative pronoun is an object.
- Keep the clause close to its antecedent and retain the relative pronoun even where English omits that.
- Relative and interrogative kiu have the same forms but different functions.
- The relative clause chooses tense and mood for its own meaning.
Related Topics
- Relative Case inside the ClauseA2 — How the case and preposition of kiu are determined inside the relative clause, independently of the antecedent’s role.
- Kies in Relative ClausesB1 — Use kies to connect a person or thing with something belonging to it, including the subject or object behind an action noun.
- Nonrestrictive Relative ClausesC1 — Add supplementary information about an already identifiable referent while keeping relative marking, case, and punctuation clear.
- Accusative in Relative ClausesB1 — How kiu, kio, and their plural forms take case from their role inside a relative clause, independently of the antecedent.
- Kiu: The Question/Relative Individual CorrelativeA1 — Use kiu to ask or relate which individual, adding -j for plural individuals and -n when its role requires the accusative.
- Ki-Correlative Embedded QuestionsB1 — How kiu, kio, kia, kies, kie, kiam, kial, kiel, and kiom introduce finite questions embedded inside larger clauses.