In short

A складнопідря́дне ре́чення is a main clause with a dependent (subordinate) clause hanging off it. Ukrainian ties the two together with a small set of connectors, and each one carries a job:

• що - “that”: reports a fact or content (I know that…).
• щоб - “so that / in order to”: expresses a wish or a purpose (I want you to… / I came in order to…).
• який - “which / who”: a relative pronoun that declines and points back to a noun.
• коли - “when”: sets the time.
• якщо - “if”: states a real condition.

The single most important habit: Ukrainian always fences the subordinate clause off with a comma, even where English drops it. Я знаю, що… never Я знаю що….

The rule

що (content clause). After verbs of knowing, saying, thinking, hearing and feeling, що introduces the reported content. It is a plain conjunction here (do not confuse it with the relative pronoun що “which”). The clause simply states what is the case, in whatever tense the meaning requires.

щоб (purpose and wish). Use щоб - not що - when the main clause expresses a wish, request, order or goal aimed at bringing something about. Two patterns:

• Same subject in both clauses → щоб + infinitive: Я прийшо́в, щоб допомогти́ (“I came in order to help”).
• Different subjects → щоб + the -в/-ла/-ло/-ли form of the verb: Я хо́чу, щоб ти прийшо́в (“I want you to come”). This form looks exactly like the past tense but works as a subjunctive - it never carries present or future meaning here.

який (relative clause). який is a full adjective-pronoun. It agrees with its antecedent in gender and number, but takes its case from the role it plays inside its own clause. In кни́га, яку́ я чита́ю, яку́ is feminine singular (from кни́га) yet accusative (it is the object of чита́ю). Beside it stands an indeclinable relative що, the ordinary choice in speech where no preposition is involved: авто́бус, що йде до це́нтру. It never changes shape and never takes a preposition — as soon as one is needed, only яки́й will do. The clause is always set off by commas.

коли (time clause). коли links an event to a time: Коли́ наста́не весна́… (“When spring comes…”). With future meaning Ukrainian uses a genuine future in both clauses - unlike English, which says “when spring comes” with a present.

якщо (condition clause). якщо states a real, possible condition: Якщо́ бу́де дощ… (“If it rains…”). For an unreal / hypothetical condition Ukrainian switches to якби + the particle би/б (see the conditional mood) - keep the two apart.

The subordinate clause may follow the main clause, precede it, or sit inside it; the comma marks the seam in every case.

Forms & patterns

Connectors at a glance

Declension of «яки́й» (declines like a hard-group adjective; gender/number from the antecedent, case from its own clause)

(Accusative has two forms for masculine and plural: inanimate = nominative-like, animate = genitive-like.)

«щоб» + verb form (verb «зроби́ти», different-subject pattern)

Examples

Common mistakes

• Я думаю що це правда -> Я ду́маю, що це пра́вда - a subordinate clause is always separated by a comma in Ukrainian, even when English omits “that”.
• Я хочу, що ти допоміг -> Я хо́чу, щоб ти допомі́г - verbs of wishing, asking and ordering take щоб (a goal), not що (a fact).
• Мама сказала, щоб ти прийдеш -> Ма́ма сказа́ла, щоб ти прийшо́в - after щоб the verb wears the -в/-ла/-ли coat; it is never present or future.
• Книга, який я читаю -> Кни́га, яку́ я чита́ю - який agrees in gender/number with кни́га (fem. sg. → яку́) but takes accusative from its own clause.
• Дім, який я живу -> Дім, у яко́му я живу́ - the relative pronoun keeps the case (and preposition) its role demands; “live in” needs locative у яко́му.
• Якщо б я був багатий, я подорожував би -> Якби́ я був бага́тий, я подорожува́в би - an unreal condition uses якби; якщо is only for real, possible ones.

Tips

• Comma first: mentally drop a comma the moment you reach що, щоб, який, коли, якщо. If the subordinate clause sits in the middle, fence it with commas on both sides.
• що = a fact, щоб = a goal. Quick test: if you could say “in order to” in English, use щоб.
• Purpose with one subject → щоб + infinitive; with two subjects → щоб + -в/-ла/-ли form. Я прийшо́в, щоб поба́чити vs Я прийшо́в, щоб ти поба́чив.
• Treat який as an adjective on a leash: it borrows gender and number from the noun it points back to, but earns its case from the job it does in its own clause.
• Future after коли and якщо: Ukrainian says коли́ при́йдеш / якщо́ при́йдеш (“when/if you will come”), where English keeps the present.
• Keep якщо (real “if”) apart from якби (hypothetical “if”, with би/б) - the second belongs to the conditional mood.
• Word order is free: the main or the subordinate clause may lead. The connector plus comma, not position, marks the dependency.