An infinitive clause is dependent on the main clause of the sentence for its meaning.

It has no grammatical subject, only an implied one, and therefore no conjugated verb.

Verbs in a main clause that often introduce an infinitive clause:

to plan/intend/decide/hope to do something

to be in the mood/interested to do something

to have the desire to do something

to forget to do something

to start/stop to do something

to ask somebody to do something

to allow somebody to do something

to forbid somebody to do something

to refuse to do something

to offer/advise to do something

to try/promise/suggest to do something

to have the possibility/opportunity to do something

 

it is nice/hard/difficult/complicated etc. to do something

The infinitive, preceded by the word "zu", goes to the end of the infinitive clause, e.g.

Sie plant, nach Deutschland zu fahren. (She plans to travel to Germany.)

Ich hoffe, meinen Freund auf der Party zu treffen. (I hope to meet my friend at the party.)

Er vergisst immer, seine  Hausaufgaben zu machen. (He always forgets to do his homework.)

If the verb in question has a separable prefix, the "zu" goes between the prefix and the stem of the infinitive, e.g.

aufstehen, er steht auf: Sie plant, morgen früher aufzustehen. (She plans to get up earlier tomorrow.)

ankommen, er kommt an: Ich hoffe, bald in Berlin anzukommen. (I hope to arrive soon in Berlin.)

mitnehmen, er nimmt mit: Er vergisst immer, seinen Regenschirm mitzunehmen. (He always forgets to bring his umbrella.)

An infinitive clause that contains only the verb and possibly an adverb is not set off by a comma, while those with other elements usually are, e.g.

Ich plane zu bleiben. (I plan to stay.)

Ich plane, drei Tage in Frankfurt zu bleiben. (I plan to stay three days in Frankfurt.)

An infinitive clause can take on the role of the subject, e.g.

Nachhaltig zu leben, ist keine leichte Sache. (It's not easy to live sustainably.)

 

Note: In English, in order to state a desire for somebody else to do something, this other person becomes the direct object of the clause, e.g. I want you to leave the house. In German, you don't use an infinitive clause but a subordinate clause starting with "dass", and this other person is the subject of that subordinate clause, e.g. Ich möchte, dass du das Haus verlässt.

Infinitive clauses with "um ... zu"

In German, you use "um ... zu" (in order to) to express an intention, e.g.

Joachim verbringt den Sommer in Dublin. Warum macht er das? Er möchte sein Englisch verbessern.

Joachim verbringt den Sommer in Dublin, um sein Englisch zu verbessern.

(Joachim spends the summer in Dublin, in order to improve his English.)

 

Infinitive clauses with "ohne ... zu" (without doing something) and "(an)statt ... zu" (instead of doing something)

Johanna geht über die Straße. Was macht sie nicht? Sie schaut nicht nach links und nach rechts.

Johanna geht über die Straße ohne nach links und nach rechts zu schauen.

(Johanna crosses the road without looking to the left and the right.)

 

Jens besucht seinen Freund. Was wäre die Alternative? Er lernt für seine Prüfung. Aber das macht er nicht.

Jens besucht seinen Freund, anstatt für seine Prüfung zu lernen.

(Jens visits his friend instead of learning for his exam.)

An infinitive clause with "um ... zu", "ohne ... zu" or "(an)statt ... zu" can came before the main clause, then the main clause startes with the conjugated verb, e.g.

Um fit zu bleiben, fährt Jana jeden Tag mit dem Fahrrad zur Arbeit. (In order to stay fit, Jana cycles to work every day.)

Ohne zu zögern, drückte Julia auf die Klingel. (Without hesitating, Julia rang the bell.)

Anstatt das Geschirr abzuwaschen, ging Jutta ins Kino. (Instead of washing the dishes, Jutta went to the cinema.)

 

Note: An infinitive clause with "um ... zu", "ohne ... zu" or "(an)statt ... zu" is always set off by a comma.