Relative Clauses: který, jenž, co

A relative clause adds information about a noun: "the man who came," "the book that I'm reading," "the house I live in." In Czech every relative clause is fenced off by commas and introduced by a relative pronoun — most often který. The one thing you must master here, and the thing that trips up nearly every English speaker, is that který splits its agreement between two clauses: it takes its gender and number from the noun outside (the antecedent) but its case from its own job inside the relative clause. Get that split right and relative clauses become fully predictable. This page is the hub; the individual pronouns get fuller treatment on their own pages.

The core mechanism: split agreement

Here is the rule you will use every single time, so read it slowly:

který agrees in gender and number with the noun it refers to (the antecedent, which is outside the relative clause), but takes its case from its own role (subject, object, after a preposition…) inside the relative clause.

The gender and number come from out there; the case comes from in here. Two different clauses, two different jobs. English pronouns barely inflect at all ("who/whom/which/that"), so English gives you no practice with this — which is exactly why it feels unnatural at first.

Watch it work on one masculine antecedent, muž ("man"), across four different in-clause roles. The gender/number stays masculine singular throughout; only the case shifts, driven by what the inner clause needs:

In every one of those, the antecedent is masculine singular, so we start from the masculine singular column of který; then the inner clause tells us the case. Přišel has který as its subject → nominative který. Pomoct governs the dative → kterému. Ve forces the locative → ve kterém.

který is declined like a hard adjective

Který / která / které declines exactly like a hard adjective (mladý type), so if you can decline an adjective you can decline který. Full paradigms live on the který declension page; here are the forms you'll reach for most:

Now watch the gender change with the antecedent, while the in-clause role stays "direct object" (accusative) each time:

Note the animacy wrinkle in the masculine accusative: an animate masculine antecedent gives kterého ("muž, kterého znám"), but an inanimate masculine gives který ("film, který znám"), because masculine inanimate accusative looks like the nominative. This is the same animacy split you meet all over the case system (see the seven cases and their questions).

Prepositions sit in front of který — and inside the clause

When the relative pronoun is governed by a preposition, the preposition comes immediately before který and lives inside the relative clause. The preposition determines the case, exactly as it would for any noun.

English can strand the preposition at the end ("the table the books lie on"). Czech cannot — the preposition must stand in front of its pronoun: na kterém, never který … na. This is a hard structural difference; you always front the preposition.

jenž — the literary equivalent

Jenž / jež / jenž is a (literary)/(formal) relative pronoun, common in books, journalism, and elevated prose, essentially interchangeable with který in meaning. It follows the same split-agreement logic — gender/number from the antecedent, case from inside the clause — but its forms are less transparent, and after prepositions it takes an -ň- shape (němž, nímž, níž). It's covered in full on the literary jenž page; a taste:

Recognise jenž/jež/jehož/němž when reading, but in speech and everyday writing use který — reaching for jenž in casual conversation sounds bookish.

co — the colloquial all-purpose relative

In (informal) spoken Czech, co serves as an invariable, catch-all relative — "the film co we saw." It doesn't decline, which is precisely why casual speech likes it, but it's out of place in formal writing.

When co stands in for an object with a preposition, colloquial speech props it up with a resumptive pronoun: ten kluk, co jsem s ním mluvil ("that boy I spoke with," literally "…that I spoke with him"). This is characteristic of relaxed spoken Czech; in writing, use který.

kdo and co after "everyone / everything / nothing"

After indefinite and demonstrative heads meaning everyone/everything/nothing/the one who, Czech uses the relatives kdo (for persons) and co (for things) rather than který. These are the "free relative" heads:

Both kdo and co still decline for their in-clause case ("ten, komu jsem to dal" — "the one to whom I gave it," dative). The ten … kdo/co and ten … který correlative patterns are worth a page of their own; see the correlative ten … který.

"whose": jehož, jejíž, jejichž

English "whose" as a relative ("the man whose car…") is expressed by the possessive relative forms jehož (his), jejíž (her), jejichž (their). These agree in gender/number/case with the possessed thing (like any possessive), while their stem (jeho-/její-/jejich-) reflects the possessor's gender/number — a double agreement that repays careful attention (full treatment on the čí / whose page).

The key thing English speakers miss: unlike the indeclinable possessive pronouns jeho/její/jejich, the relative jejíž does inflect — jejíž syn (nom.), jejíhož syna (acc.) — because it agrees with the possessed noun's case.

The comma rule

Every relative clause is set off by commas — one to open it, and if it's embedded, a second to close it. This is not optional and not by feel: Czech commas by structure (see subordinate clauses and the comma rule). The commonest slip is dropping the closing comma of an embedded clause.

In Auto, které jsem koupil, je červené, the relative clause is bracketed on both sides, and only then does the main predicate je červené resume. English ("The car I bought is red") uses no commas at all — do not let that habit erase the Czech ones.

Common Mistakes

Key Takeaways

• The everyday relative is který / která / které, declined like a hard adjective.
• Split agreement is everything: gender and number come from the antecedent (outside), case from the pronoun's role inside the relative clause.
• Watch the masculine accusative animacy split: kterého (animate) vs který (inanimate).
• Czech never strands prepositions — front them before the pronoun: ve kterém, s nímž, o kterém.
• jenž/jež is the (literary) equivalent; co is the (informal) invariable relative; kdo/co follow ten, všechno, každý, nic.
• Relative "whose" is jehož / jejíž / jejichž — and unlike plain jeho/její/jejich, jejíž inflects.
• Fence every relative clause with commas — both sides if it's embedded.