Iu refers to an unidentified or unspecified individual: “someone,” “somebody,” “some one,” or, before a noun, “some.” It selects an individual without identifying which member of the relevant set it is. All unmarked uses on this page are neutral in register.
The indefinite-individual cell
The table-word system combines five initial meanings with nine semantic domains. The initial i- contributes indefiniteness: the speaker does not identify a particular value. The ending -u selects an individual and its identity. Thus iu means “some individual.”
| Form | Force over individuals |
|---|---|
| kiu | which individual? |
| tiu | that identified individual |
| iu | some unidentified individual |
| ĉiu | each/every individual |
| neniu | no individual |
This architecture matters because English “someone,” “something,” “some kind,” and “some amount” all begin with some- but occupy different Esperanto cells: iu, io, ia, and iom.
Iu frapis ĉe la pordo, sed kiam mi malfermis, neniu estis tie.
Someone knocked at the door, but when I opened it, nobody was there.
Mi bezonas ion por skribi kaj iun, kiu konas la adreson.
I need something to write with and someone who knows the address.
Standing alone and preceding a noun
Used alone, iu has an understood noun. If context supplies no other category, people normally interpret it as “some person.” Context can instead make a thing or another countable individual understood.
Ĉu iu povas helpi min porti ĉi tiun tablon?
Can someone help me carry this table?
El la tri ŝlosiloj, iu certe malfermos la malantaŭan pordon.
Of the three keys, one of them will surely open the back door.
Before a noun, iu is a determiner. It marks the noun phrase as indefinite but individual: the speaker selects one or more members without telling the listener exactly which. Because iu itself is a determiner, it does not combine with la.
Mi vidis iun malnovan konaton en la stacidomo, sed mi ne povis memori lian nomon.
I saw an old acquaintance at the station, but I could not remember his name.
Iuj najbaroj jam subskribis la peticion; aliaj ankoraŭ pripensas ĝin.
Some neighbors have already signed the petition; others are still considering it.
Do not treat iu as Esperanto's general indefinite article. A bare noun already expresses ordinary English “a/an”: Mi aĉetis libron means “I bought a book.” Mi aĉetis iun libron adds deliberate non-identification: some particular book, but its identity is unknown, unimportant, or withheld.
Mi serĉas hotelon proksime al la stacidomo.
I am looking for a hotel near the station.
Mi serĉas iun hotelon, kies nomon mi forgesis.
I am looking for some hotel whose name I have forgotten.
Number and accusative marking
Unlike most table-word endings, -u permits both plural -j and accusative -n. The complete paradigm is regular:
| Non-accusative | Accusative | |
|---|---|---|
| singular | iu | iun |
| plural | iuj | iujn |
When iu modifies a noun, eligible adjectives and the noun show the same number and case.
Ĉu vi invitis iun novan kolegon? — Jes, mi invitis du novajn kolegojn.
Did you invite some new colleague? — Yes, I invited two new colleagues.
Mi rekonis iujn el la fotoj, sed ne ĉiujn.
I recognized some of the photos, but not all of them.
In iuj el la fotoj, iuj selects several individuals from a definite set. This is different from iom de la materialo, which selects an amount rather than countable members.
Questions, negation, and scope
In a yes–no question, iu commonly means “someone/anyone”: it asks whether at least one individual satisfies the description. Esperanto does not need a separate “any” word simply because the clause is interrogative.
Ĉu iu vidis mian bluan jakon? — Jes, Marta portis ĝin al la akceptejo.
Has anyone seen my blue jacket? — Yes, Marta took it to reception.
For an unrestricted negative, use the negative-series form neniu. Esperanto normally expresses the zero individual directly rather than combining clause negation with iu.
Neniu respondis al la mesaĝo.
Nobody answered the message.
Ne iu is possible only when ne rejects the choice “some particular individual,” usually in an explicit correction. It does not serve as the routine translation of English “nobody.”
Ne iu gasto prenis la mantelon, sed la kelnero movis ĝin.
It wasn't some guest who took the coat; the waiter moved it.
That marked contrastive construction belongs to focus and correction. The neutral negative is Neniu gasto prenis la mantelon.
Iu versus neighboring choices
Use iu for identity, io for an unnamed thing or matter, and ia for kind or quality. Use unu when the number one is central or when contrasting one member with another.
Iu lasis ion sur la tablo: ian malgrandan aparaton.
Someone left something on the table: some kind of small device.
Unu el la lampoj ne funkcias, sed mi ne scias, kiu.
One of the lamps does not work, but I do not know which one.
The first sentence moves from an unidentified individual (iu) to an unnamed thing (io) and then classifies its kind (ia aparato). The second counts exactly one lamp; unu therefore matters.
Iu ajn means any individual without restriction: identity makes no difference. That free-choice construction is productive and neutral, but its scope is treated fully on the ajn for free choice page.
Common Mistakes
Using io for a person
❌ Io atendas vin ĉe la enirejo.
Incorrect for an unidentified person — io means an indefinite thing or matter.
✅ Iu atendas vin ĉe la enirejo.
Someone is waiting for you at the entrance.
Omitting agreement
❌ Mi renkontis iu afabla instruisto.
Incorrect — the direct-object phrase needs accusative marking throughout.
✅ Mi renkontis iun afablan instruiston.
I met a kind teacher whose identity is not being specified.
❌ Iu studentoj ankoraŭ laboras en la biblioteko.
Incorrect for several students — iu must take plural -j.
✅ Iuj studentoj ankoraŭ laboras en la biblioteko.
Some students are still working in the library.
Combining iu with the article
❌ La iu viro demandis pri vi.
Incorrect — iu and la are both determiners.
✅ Iu viro demandis pri vi.
Some man asked about you.
Copying English negative “any”
❌ Mi ne vidis iun en la oficejo.
Misleading as a neutral total negative; it can suggest contrastive ‘not someone.’
✅ Mi vidis neniun en la oficejo.
I saw nobody in the office.
Key Takeaways
Iu selects an unidentified individual and can stand alone or determine a noun. It takes -j and -n as meaning and syntax require. Use bare nouns for ordinary English indefinite articles, neniu for an unrestricted negative, io for an unnamed thing, and ia for an unspecified kind.
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Start learning Esperanto →Related Topics
- 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.
- Tiu: The Demonstrative Individual CorrelativeA2 — Point out particular people or things with tiu, including its determiner, standalone, plural, accusative, and relative-pair uses.
- Io: The Indefinite Thing CorrelativeB1 — Use io for an unnamed thing, fact, or matter, with accusative marking, postposed modifiers, and no ordinary plural.
- Neniu: The Negative Individual CorrelativeC1 — Use neniu to exclude every individual in a relevant set, with correct case, number, determiner behavior, and negation scope.
- Case and Number on CorrelativesA2 — Learn exactly which correlative families accept plural -j, object -n, or directional -n, and which remain invariant.