In short

Być (“to be”) is the single most important verb in Polish, and it is irregular, so you must memorize its forms. It links a subject to a description, a place, or another noun, and it is also the building block of the compound future tense (Lesson 22). Learn its present, past, and future by heart now and the rest of the course stands on firm ground.

The rule

Być does not follow any of the regular conjugation groups (Lesson 5). Learn each form separately, then watch how much of Polish leans on it.

What być is used for

• Identity / description: Jestem Marta. On jest wysoki.
• Origin: Jesteśmy z Polski.
• Location: Kot jest w ogrodzie.
• Linking to another noun (see the case rule below): Ona jest lekarką.

The Instrumental predicate - a key Polish rule

When być joins the subject to a noun (“X is a Y”), that predicate noun goes into the instrumental case (Lesson 10), not the nominative:

• Jestem studentem. (I am a student - masc.)
• Ona jest nauczycielką. (She is a teacher - fem.)

But when the predicate is an adjective, it stays in the nominative and simply agrees in gender and number with the subject:

• Jestem zmęczony. (masc.) / Jestem zmęczona. (fem.) - I am tired.

to jest / to są - pointing at things

To point something out (“this is / these are”), Polish uses the fixed frame to jest / to są. Here the noun stays in the nominative, because to (“this”) is the real subject:

• To jest książka. (This is a book.) - nominative, not instrumental.
• To są moje klucze. (These are my keys.)

Dropping the pronoun

Because each ending already shows the person, the subject pronoun is usually dropped and used only for emphasis or contrast: Jestem gotowy rather than Ja jestem gotowy.

Forms & patterns

Present tense (czas teraźniejszy)

Negate by putting nie before the verb: nie jestem, nie ma jej tu (note: “there is no X” uses nie ma + genitive, an idiom you will meet in Lesson 15).

Future tense (czas przyszły) - być is the base of the compound future

Past tense (czas przeszły) - gendered, mobile endings

The past of być is built on the stems był- (singular) and byl-/był- (plural), and the endings change with gender. In the plural, Polish splits into virile (masculine-personal: a group that includes at least one man) and non-virile (everything else) - see Lesson 30.

The personal endings -m, -ś, -śmy, -ście are mobile: they can detach from the verb and hop onto an earlier stressed word - Gdzie byłeś? can become Gdzieś był? (both correct). As a beginner, keep them on the verb; just recognize the pattern when you hear it.

Examples

Common mistakes

• Jestem student -> Jestem studentem - a predicate noun after być takes the instrumental case.
• Ona jest nauczycielka -> Ona jest nauczycielką - same rule: instrumental, not nominative.
• To jest książką -> To jest książka - after to jest the noun stays nominative.
• Ja jestem, ty jesteś, on jest zmęczony said with every pronoun -> drop the pronoun: Jestem zmęczony - the ending already shows who.
• Byłem used by a woman -> Byłam - the past tense must match your gender.
• Będę jestem w domu -> Będę w domu - the future będę already means “I will be”; do not add a second być.

Tips

• Drill the six present forms aloud until they are automatic - you will use być in almost every lesson from here on.
• One quick test for the case: noun after być -> instrumental (Jestem lekarzem); adjective after być -> nominative (Jestem chory).
• To jest / to są is the everyday way to say “this is / these are” - and it keeps the noun in the plain nominative you already know.
• Remember that the past tense carries gender: a man says byłem, a woman says byłam, and the plural splits into virile byli vs. non-virile były.
• Będę, będziesz, będzie… is not just “I will be” - these forms also build the compound future of other verbs (Lesson 22), so this paradigm pays off twice.