sein carries more grammatical weight than any other verb in German. It is irregular, it is everywhere, and it does two completely different jobs: one as a copula that holds both sides of a sentence in the Nominativ, and one as the auxiliary verb that forms the Perfekt of movement and change.
The forms: Präsens
sein is fully irregular. The forms have to be learned individually. None of them follow a regular pattern.
| Person | Form |
|---|---|
| ich | bin |
| du | bist |
| er · sie · es | ist |
| wir | sind |
| ihr | seid |
| sie · Sie | sind |
The forms: Präteritum
In the past, sein mostly uses Präteritum, not Perfekt. Nobody usually says Ich bin der Freund gewesen in normal speech. war is the standard form, in every situation, spoken and written.
| Person | Form |
|---|---|
| ich | war |
| du | warst |
| er · sie · es | war |
| wir | waren |
| ihr | wart |
| sie · Sie | waren |
Job 1: copula verb
sein is the main copula verb in German. It does not transfer action to an object. It equates. It says what something is. Because nothing is transferred, nothing changes case. Both sides of the sentence stay in the Nominativ.
- Ich binein Lehrer. (I am a teacher.)
- Er istder Chef. (He is the boss.)
- Das istein Problem. (That is a problem.)
After sein, the noun that follows stays in the Nominativ. It is not an object. It is a description that comes back to the subject from the other side.
Job 2: auxiliary verb in Perfekt
sein is also an auxiliary verb. It forms the Perfekt together with the past participle. But not for every verb. sein is used as auxiliary for two groups only: verbs that express movement from one place to another, and verbs that express a change of state.
| Group | Example verbs |
|---|---|
| Movement A to B | gehen fahren fliegen laufen kommen reisen schwimmen |
| Change of state | werden wachsen sterben erschrecken |
| A few extras | bleiben passieren sein |
- Ich bin nach Hause gegangen. (I went home.)
- Er ist nach Berlin gefahren. (He drove to Berlin.)
- Sie ist um 7 Uhr aufgewacht. (She woke up at 7.)
- Wir sind drei Tage geblieben. (We stayed for three days.)
For everything else, the auxiliary is haben. When in doubt, ask: did it go from A to B, or did something change? If yes → sein. If no → haben.
sein is irregular in Präsens (bin, bist, ist, sind, seid, sind) and always uses Präteritum in the past (war, warst...). As a copula it keeps both sides Nominativ. As an auxiliary it forms the Perfekt of movement and change.