Predicate Nominative with Být

When you say X is Y in Czech — Prague is beautiful, that's my brother, she's a teacher — you join two things with the verb být (to be). The first job of this page is a reassuring one: in the classic case, the thing after být stands in the nominative, exactly like the subject. So for X is Y, you can think nominative = nominative. The second job is to warn you about the one big complication an A2 learner needs to recognise: for professions, roles and changeable states, the instrumental competes with the nominative. We will point at it here and treat it in full on the instrumental predicate page.

The grammatical term for the word after a linking verb is the predicate — the predicate noun (bratr) or predicate adjective (krásná). With být, that predicate is not an object the way the thing you see or buy is an object. It does not get the accusative. It mirrors the subject, and the default mirror is the nominative.

Subject and predicate share the nominative

Both halves of an identity sentence sit in the nominative. The verb být is just an equals sign between them.

Here můj bratr Tomáš is the predicate noun, and every word of it is nominative — the same form you would use if bratr were the subject. The little word to (this/that) is a fixed pointing word, not a separate subject to worry about.

The verb ending -m in jsem already carries the "I", so there is no já; student is the predicate noun, nominative. Compare English, which forces a student with an article — Czech has none, so the bare nominative noun does all the work.

Predicate adjectives stay nominative and agree

When the predicate is an adjective, it stays in the nominative and agrees with the subject in gender and number — exactly as an adjective agrees with its noun. This is where English speakers, used to an invariable is tall, must add an ending.

Change the gender of the subject and the adjective shifts with it: Je vysoký (he is tall) but Je vysoká (she is tall), To auto je nové (that car is new, neuter). The verb být never changes for gender in the present — the agreement lives in the adjective.

Never drop být, never use the accusative

Two transfer errors are worth fixing now. First, být cannot be dropped. Some languages omit "to be" in the present ("he tall", "this my brother"), and learners carry that habit over. Czech keeps the verb in every plain statement.

Second, the predicate after být is not an accusative object. English hides this because its nouns do not change, but its pronouns expose a clash: English says It's me, It's him with object pronouns, while Czech uses the nominative — and even makes the verb agree with that pronoun.

Where the instrumental competes

For professions, roles and functions — and obligatorily after verbs of becoming — Czech offers the instrumental as an alternative to the nominative. With plain být, both are grammatical, but they have a different flavour: the nominative states a permanent identity ("this is what he is"), while the instrumental frames a role or function ("this is the capacity he acts in"), and tends to feel more formal or more tied to a particular time.

After stát se (to become), být in the sense of acting as, and similar change-of-state verbs, the instrumental is not optional — this is the one place you cannot fall back on the nominative.

Common mistakes

Key takeaways

• After plain být, both the subject and the predicate noun/adjective stand in the nominative — think nominative = nominative for X is Y.
• A predicate adjective agrees in gender and number: Praha je krásná, ten film byl dlouhý, to auto je nové.
• Czech keeps být in every statement and uses nominative pronouns where English uses object forms: To jsem já, not To je mě.
• For professions and roles the instrumental competes (je inženýrem), and after stát se it is obligatory (stal se lékařem) — but the nominative is the safe default for identity at A2.