In short

Indefinite pronouns are the words for someone, something, some, anyone, anything, any — when you don’t name a specific person or thing. Ukrainian builds them by bolting a small particle onto a question word (хто “who”, що “what”, який “which”, чий “whose”, де “where”, коли “when”). The three particles you meet most are:

• -сь / -ось — the everyday “some-” (there IS such a person/thing, you just don’t specify): хтось “someone”, щось “something”.
• будь- — the free-choice “any-” (it doesn’t matter which one): будь-хто “anyone at all”.
• -не́будь — a looser “any-”, often in questions and the future: хто-не́будь “anyone / someone or other”.

The question word inside keeps declining exactly as it does on its own; the particle just rides along.

The rule

Take an interrogative pronoun (хто, що, який, чий) or a pro-adverb (де, куди, коли, як) and attach a particle. Which particle you choose sets the meaning:

1. -сь (also spelt -ось after some forms) = “some-”, definite-but-unnamed. There exists a specific someone/something; the speaker either doesn’t know or doesn’t say which. This is the default translation of English someone / something in a statement.

Хтось телефонува́в. — Someone called.

2. будь- (a prefix, joined with a hyphen) = “any-”, absolutely free choice. Any candidate will do; it makes no difference which. Strong, emphatic “anyone at all”.

Спита́й будь-кого́. — Ask anyone (at all).

3. -не́будь (a suffix, joined with a hyphen) = “any- / some-”, vague choice. Similar to будь- but softer and more colloquial; very common in questions, requests and future plans where the referent isn’t fixed yet.

Розкажи́ що-не́будь. — Tell me something (or other).

Two more particles, less frequent but worth recognising — and, unlike будь-, both are written as one word:

4. де- (prefix) = “a certain, some” — rare, bookish. де́хто “some people, a certain someone”, де́що “a few things, something”. 5. аби- (prefix) = “any old, just any” — dismissive “no matter which”. аби́хто “just anybody”, аби́що “any old thing, trifle”.

Key point for an English speaker: the particle itself never declines (only -сь appears as -ось after a consonant); the question word inside does. So “someone” in the accusative is кого́сь, in the dative кому́сь — сь simply stays glued to the end. With будь- and -небудь the hyphen stays and the core word declines: будь-кому́, кому́-не́будь.

Forms & patterns

The base question words (declension of хто and що)

Everything else is built on these. Learn this paradigm and you can build every indefinite pronoun.

Series 1 — the -сь pronoun (хтось “someone”)

The particle -сь stays; the хто-part declines as above.

Series 2 — будь- pronoun (будь-хто “anyone”)

The prefix будь- and the hyphen stay; the хто-part declines.

Series 3 — -небудь pronoun (хто-небудь “anyone / someone”)

The suffix -небудь and the hyphen stay; the хто-part declines.

The adjective-type pronoun який “which/some”

яки́йсь “some (kind of)”, будь-яки́й “any”, який-небудь “any/some” agree with their noun in gender, number and case like an ordinary adjective; the particle rides on the end (or, for будь-, on the front).

Pro-adverbs (bonus set)

The same particles build indefinite adverbs — no declension, they’re invariable.

Examples

Common mistakes

• хтось-то -> хтось — Ukrainian has no -то particle here (that’s Russian «кто-то»); use plain -сь.
• хтось подзвонив когось -> хтось подзвони́в кому́сь — the inner word must take its case: “someone phoned to someone” needs dative комусь, not accusative.
• будьхто / будь хто -> будь-хто — будь- is always joined with a hyphen, never fused and never a separate word.
• хтонебудь / хто небудь -> хто-не́будь — -небудь is always hyphenated to the question word.
• будь-хто не прийшов -> ніхто не прийшо́в — for “nobody came” you need the negative pronoun ніхто, not будь-хто; будь- pronouns are not negatives.
• Я не бачив когось -> Я не ба́чив ніко́го — under negation Ukrainian switches to the ні- series with double negation, not to хтось.
• якийсь книга -> яка́сь кни́га — the який-type pronoun must agree in gender: fem. якась.
• щось цікаве трапилася -> щось ціка́ве тра́пилося — щось is neuter, so the verb and adjective take neuter agreement.

Tips

• Memory hook for the three cores: -сь = “some” (it exists), будь- = “be it whoever” (free choice), -небудь = “who-knows-which” (vague). English some- usually maps to -сь; any- maps to будь-/-небудь.
• Decline the inside word, park the particle. If you can say кого́сь, кому́сь, ки́мось, you’ve mastered the whole -сь series — the same trick works for що, який, чий, and even де/коли.
• будь- and -небудь always take a hyphen; -сь/-ось, де- and аби- never do — хтось, де́хто, аби́що are each one word. Get the hyphens right and the spelling is done.
• In questions and future plans, prefer -небудь: Ти ку́пиш що-не́будь? “Will you buy anything?” It sounds more natural there than щось, though щось is not wrong.
• Do not reach for these under negation. “I saw nobody” is not будь-кого or когось but ніко́го, with не before the verb (see the negative-pronouns lesson).
• Watch the shape of the particle: it is -сь almost everywhere (хтось, щось, кого́сь, яки́йсь), but -ось after the м of the instrumental (ки́мось, чи́мось, яки́мось) — and never the Russian -то.
• будь- can also front whole phrases: будь-яки́м спо́собом “by any means”, будь-де “anywhere at all” — a handy, emphatic pattern.