What are auxiliary verbs?
German has three auxiliary verbs: sein, haben and werden. All three can also act as full verbs with their own meaning. As auxiliaries, they help build tenses: combined with a full verb, they express past, future or passive.
For the Perfekt and Plusquamperfekt you need sein or haben. Werden is used for Futur I, Konjunktiv II and the Vorgangspassiv. For the Zustandspassiv you use sein again.
As a full verb, sein/haben/werden stand alone: Er hat ein Fahrrad. As an auxiliary, they combine with another verb: Er hat das Buch gelesen.
Present tense conjugation
All three auxiliary verbs are irregular. In the present tense their forms differ greatly from the infinitive.
sein: Uses
When do you use sein?
You use sein as an auxiliary in the Perfekt and Plusquamperfekt with verbs that describe a change of place or a change of state. Also with: passieren, bleiben, geschehen, sein, werden, gelingen.
As a full verb, sein describes a state or a characteristic.
In the Zustandspassiv, sein combines with the past participle to describe the result of a process.
haben: Uses
Haben is the most common auxiliary in German. It forms the Perfekt and Plusquamperfekt of most verbs.
When do you use haben?
All verbs that don't describe a change of place or state form the Perfekt with haben. This also applies to verbs with an accusative object, even when they describe movement.
"Er ist mit dem Auto gefahren" (movement) vs. "Er hat das Auto gefahren" (the car as object). With an accusative object, always haben.
As a full verb, haben expresses possession.
werden: Uses
Werden plays several roles in German: as an auxiliary it forms Futur I, Konjunktiv II and the Vorgangspassiv.
Futur I: werden + infinitive
With werden + infinitive you express something happening in the future, or a guess about the present.
Konjunktiv II
For wishes and hypotheticals you use the Konjunktiv II forms of werden (würde), sein (wäre) and haben (hätte).
Vorgangspassiv: wird + past participle
The Vorgangspassiv describes an ongoing process. You form it with werden + past participle.
As a full verb, werden expresses a process or change.
Exercises
Auxiliary or full verb? Look at the bold verb. Does it stand alone? Or is it helping another verb to form a tense?
Auxiliary or full verb?
Look at the bold verb and choose the correct category.