This is the single most important rule of the instrumental, and one of the most counter-intuitive facts in all of Polish for an English speaker. When you say what someone is — their profession, identity, role, or nature — the noun after być ("to be") does not stay in the dictionary form. It goes into the instrumental: Jestem nauczycielem ("I am a teacher"), not jestem nauczyciel. English has exactly one verb "am" and never inflects what follows it, so the idea that "a teacher" should appear in a special case after "I am" feels almost nonsensical at first. But once you grasp why — and learn the one big exception (predicate adjectives) and the one big counter-construction (to jest) — you can produce these sentences automatically.
The core rule: być + NOUN (identity/role) → instrumental
When the verb być links a subject to a noun that names what the subject is — a job, a role, an identity, a category — that predicate noun takes the instrumental case (-em for masculine/neuter, -ą for feminine).
| Nominative (dictionary form) | Instrumental (predicate) | Sentence |
|---|---|---|
| nauczyciel | nauczycielem | Jestem nauczycielem. |
| lekarka (f.) | lekarką | Ona jest lekarką. |
| student | studentem | Mój brat jest studentem. |
| inżynier | inżynierem | Chcę być inżynierem. |
Jestem nauczycielem w liceum, uczę historii.
I'm a teacher at a high school, I teach history.
Moja siostra jest lekarką w szpitalu na Mokotowie.
My sister is a doctor at a hospital in Mokotów.
Kim jesteś z zawodu? — Jestem programistą.
What do you do for a living? — I'm a programmer.
Notice the question word: kim jesteś? ("who/what are you?") — kim is itself the instrumental of kto, and the question form already signals the case the answer must take. If a Pole asks you kim jesteś?, the grammar of the answer is half-decided for you: the role-noun comes back in the instrumental.
The big exception: być + ADJECTIVE → nominative
Here is the rule that saves you from over-applying the instrumental. When what follows być is an adjective — describing a quality, state, or property rather than naming a category — it stays in the nominative and simply agrees with the subject in gender and number. It does not go instrumental in normal modern speech.
| Type of predicate | Case | Example |
|---|---|---|
| Noun (identity/role) | Instrumental | Jestem lekarzem. (I'm a doctor.) |
| Adjective (quality/state) | Nominative | Jestem zmęczony. (I'm tired.) |
Jestem bardzo zmęczony, idę spać.
I'm very tired, I'm going to bed.
Ona jest miła i bardzo zdolna.
She is nice and very capable.
Jesteśmy głodni — zamówmy coś do jedzenia.
We're hungry — let's order something to eat.
So the case depends entirely on noun versus adjective, not on the verb. Jestem lekarzem (noun → instrumental) but jestem chory (adjective → nominative, "I'm ill"). A native speaker would never say jestem chorym in ordinary conversation to mean "I'm ill" — chorym as a free adjective predicate sounds wrong or archaic. (You will hear instrumental adjectives when the adjective is glued to a noun phrase that's already instrumental, e.g. jest dobrym lekarzem "he's a good doctor" — but there the adjective is just agreeing with the instrumental noun lekarzem; the trigger is still the noun.)
"Become" and "turn out to be": zostać, okazać się, stać się
The instrumental predicate isn't limited to być. A small family of "becoming" and "appearing-to-be" verbs governs the same instrumental, because they all link a subject to a role or category it moves into or is revealed to be.
| Verb | Meaning | Example |
|---|---|---|
| zostać | become (step into a role/title) | Został prezydentem. |
| stać się | become (turn into; more gradual/abstract) | Stał się bohaterem. |
| okazać się | turn out to be | To okazało się błędem. |
| być / bywać | be / be (habitually) | Bywa czasem dziwakiem. |
W zeszłym roku został dyrektorem firmy.
Last year he became the director of the company.
Chciałabym kiedyś zostać pisarką.
I'd like to become a writer someday.
Cała ta historia okazała się wielkim nieporozumieniem.
The whole story turned out to be a big misunderstanding.
Zostać + instrumental is the standard way to say "become [a profession/title]" — zostać lekarzem, zostać matką, zostać mistrzem ("become a doctor / a mother / a champion"). And okazać się + instrumental ("turn out to be") is extremely common in narrative and news: to okazało się prawdą ("it turned out to be true"). Note that with okazać się, predicate adjectives also tend to go instrumental in careful registers (okazał się niewinny or okazał się niewinnym "he turned out innocent") — but with the everyday być, keep adjectives nominative.
The counter-construction: to jest + NOMINATIVE
Now the exception that confuses everyone. There is a different sentence pattern, built on the word to, where the noun is nominative, not instrumental. This is the to jest ("this is / it is") construction — used for pointing out, identifying, or introducing, rather than for stating someone's role.
| Construction | Case of noun | Function | Example |
|---|---|---|---|
| Subject + być + noun | Instrumental | states a role/identity | On jest nauczycielem. (He is a teacher [by profession].) |
| To (jest) + noun | Nominative | identifies / introduces | To jest nauczyciel. (This is the/a teacher.) |
To jest mój nowy nauczyciel hiszpańskiego.
This is my new Spanish teacher.
To jest Anna, a to jej mąż, Marek.
This is Anna, and this is her husband, Marek.
Co to jest? — To jest słownik polsko-angielski.
What is this? — This is a Polish-English dictionary.
The difference is real and meaningful. On jest nauczycielem answers "what does he do / what is he?" — it classifies him. To jest nauczyciel answers "who/what is this?" while pointing — it identifies a specific person or thing in front of you. After to (jest), the noun is a plain nominative because to is the grammatical subject ("this") and the noun is renaming it, equation-style. There is a fuller treatment of this pattern on the to jest page; here, just hold the contrast.
Common Mistakes
❌ Jestem nauczyciel.
Incorrect — a predicate noun after być takes the instrumental: jestem nauczycielem.
✅ Jestem nauczycielem.
I am a teacher.
❌ Ona jest lekarka.
Incorrect — feminine predicate noun goes instrumental in -ą: jest lekarką.
✅ Ona jest lekarką.
She is a doctor.
❌ Jestem zmęczonym.
Incorrect — a predicate adjective stays nominative and agrees: jestem zmęczony (m.) / zmęczona (f.).
✅ Jestem zmęczony.
I'm tired.
❌ To jest nauczycielem.
Incorrect — after to jest the noun is nominative: to jest nauczyciel.
✅ To jest nauczyciel.
This is the teacher.
❌ Został prezydent w wyborach.
Incorrect — zostać ('become') governs the instrumental: został prezydentem.
✅ Został prezydentem w wyborach.
He became president in the election.
Key Takeaways
- być + NOUN (profession, role, identity) → the noun goes instrumental: Jestem nauczycielem, Ona jest lekarką.
- być + ADJECTIVE (quality, state) → the adjective stays nominative: Jestem zmęczony, Jesteśmy głodni. The case follows noun-vs-adjective, not the verb.
- zostać / stać się / okazać się ("become / turn out to be") govern the same instrumental: został prezydentem, okazało się błędem.
- to jest + NOUN is a different construction — the noun is nominative because it identifies or points out: To jest nauczyciel.
- The question kim jesteś? ("who are you / what do you do?") already cues the instrumental answer.
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Start learning Polish→Related Topics
- Instrumental: FormsA2 — The instrumental (narzędnik) endings — masculine/neuter -em, feminine -ą, plural -ami (plus the -mi handful: ludźmi, dziećmi, końmi) — with the velar softening k/g→ki/gi and the crucial ą-vs-ę contrast with the accusative.
- Nominative in Predicates and NamingA2 — When 'X is Y' keeps the nominative — after to and in naming, labels and titles — versus when Polish demands the instrumental, with the decisive to/instrumental split.
- Identifying Sentences: To jest…A1 — The frozen 'this/that is' construction (To jest dom, To są moje dzieci) — why to never changes, why the predicate noun stays nominative, and how it differs from On jest nauczycielem.
- być — to beA1 — Complete reference for być ('to be') — the most essential and most irregular Polish verb: full present, past (by gender), future, imperative, conditional and verbal-adverb tables, plus its three predicate patterns.
- Instrumental: All Uses at a GlanceB1 — A single scannable reference to every job the instrumental does — means, transport, predicate noun, accompaniment with z, static location, time and manner, certain verbs — unified by one idea: the means or attendant circumstance.
- Forgetting the Instrumental After byćA2 — Why 'I am a teacher' needs the instrumental in Polish (Jestem nauczycielem), why adjectives stay nominative, and why 'to jest' keeps the nominative.