Learn when German uses an infinitive phrase with zu, how it is formed, and when modal verbs take an infinitive without zu. Practise separable verbs and replacing a dass-clause when both clauses share the same subject.
Explanation
The infinitive with **zu**
An infinitive phrase complements a main clause. It contains **zu + infinitive** and normally follows the main clause.
> Mia versucht, früher **zu schlafen**.
When do we use **zu + infinitive**?
It commonly follows impersonal expressions, nouns used with **haben**, and verbs such as **versuchen, vorhaben, versprechen, empfehlen, anfangen, aufhören**, and **sich freuen**.
| Trigger | Example |
|---|---|
| impersonal expression | Es ist sinnvoll, eine Pause **zu machen**. |
| noun with **haben** | Wir haben die Absicht, im Mai **umzuziehen**. |
| certain verb | Leo verspricht, pünktlich **anzurufen**. |
Word order and separable verbs
The infinitive phrase follows the main clause, and the infinitive is last:
> Jana hat keine Zeit, heute lange **zu kochen**.
With a separable verb, **zu** goes between the prefix and the verb stem: **anzurufen, einzukaufen, mitzubringen**.
When is there no **zu**?
Modal verbs such as **können, müssen, dürfen, sollen, wollen**, and **möchten** take a second infinitive without **zu**:
> Wir müssen jetzt **gehen**.
> Sam will morgen länger **bleiben**.
An infinitive without **zu** is also common after perception verbs such as **sehen** and **hören**, and after **lassen**.
Replacing a **dass**-clause
If the understood subject is the same in both parts, an infinitive phrase can replace a **dass**-clause:
> Nora verspricht, dass sie die Tür abschließt.
> Nora verspricht, die Tür **abzuschließen**.
If the subjects differ, the replacement is not possible: **Nora hofft, dass Paul die Tür abschließt.** (Nora hopes that Paul locks the door.)
Comma
A comma is required, among other cases, when the infinitive phrase depends on a noun such as **Absicht** or **Wunsch**, or begins with **um, ohne, statt/anstatt, außer**, or **als**. In other contexts it can be optional. This lesson uses it consistently for clarity.