zu + Infinitive and um...zu in German: The Rules

Here is the whole system in three sentences. A second verb at the end of a German sentence normally takes zu (Ich versuche, früh aufzustehen), except after modals, after werden, and after a short closed list of verbs like sehen, hören, lassen, gehen, bleiben, where the infinitive stands bare (Ich muss aufstehen, Ich höre ihn singen). With a separable verb, zu does not sit in front of the word - it climbs inside it: aufstehen becomes aufzustehen, anrufen becomes anzurufen.

The purpose constructions are the same machine with a preposition bolted on the front: um ... zu (in order to), ohne ... zu (without doing), statt/anstatt ... zu (instead of doing). All three share one non-negotiable condition: the subject of the main clause must also be the understood subject of the infinitive half. When the subjects differ, you switch to damit and a full subordinate clause. That last rule is where most B1 learners quietly go wrong for years, because the sentence still sounds fine in their head.

When the infinitive takes zu - and when it does not

The default is zu. The bare infinitive is the exception, and the exception list is short enough to memorise in one sitting.

The noun-plus-zu frames are where German feels least like English. Lust haben, etwas zu tun, keine Zeit haben, etwas zu tun, Angst haben, etwas zu tun - these behave as fixed units and are worth learning as whole chunks rather than assembling them from parts. They live on /collocations with example sentences, which is where they belong: as expressions, not as grammar exercises.

One footnote that catches people in the perfect tense: sehen, hören and lassen replace their past participle with an infinitive. Ich habe ihn kommen sehen, not gesehen. Ich habe das Auto reparieren lassen, not gelassen. This double infinitive is standard, not sloppy.

Where zu goes inside a separable verb

With a separable verb, zu is inserted between the prefix and the stem, and the whole thing is written as one word:

• aufstehen - Es ist schwer, um sechs Uhr aufzustehen.
• anrufen - Ich habe vergessen, dich anzurufen.
• vorbereiten - Wir haben angefangen, das Essen vorzubereiten.
• mitkommen - Hast du Lust mitzukommen?

Inseparable verbs do the boring thing - zu stays outside as a separate word: zu verstehen, zu besuchen, zu erklären, zu bezahlen. So the only real question is whether the prefix is stressed. AUFstehen is separable; verSTEHen is not. If that distinction is still fuzzy, fix it first in the separable verbs guide - every rule on this page depends on hearing which syllable carries the stress.

Mixed prefixes (durch-, über-, um-, unter-) follow their own verb: Ich hoffe, dich wiederzusehen* but Ich hoffe, den Text zu übersetzen*.

um ... zu, ohne ... zu, statt ... zu

All three put the preposition at the front of the clause and the zu + infinitive at the very end. Everything else - objects, adverbs, prepositional phrases - goes in the middle.

Two details that pay off immediately. First, the comma: with um, ohne, statt, anstatt, als, außer the comma is obligatory. With a plain zu-infinitive it is officially optional, but it is obligatory when the clause depends on a noun or is announced by es, darauf, daran - and native writers set it almost always. Just write it.

Second, modals do fit inside um ... zu, as the final infinitive: Ich lerne Deutsch, um in Wien arbeiten zu können**. That is a very natural B2 move and worth practising early.

The same-subject rule, and when to reach for damit

Um ... zu has no subject of its own, so it borrows the one from the main clause. That means this is wrong:

• Ich erkläre es langsam, um mein Kollege es versteht. - impossible.
• Ich erkläre es langsam, um es zu verstehen. - grammatical, but it says I want to understand it. Not what you meant.
• Ich erkläre es langsam, damit mein Kollege es versteht. - correct.

The test takes two seconds: name the person doing the main action, then the person doing the purpose action. Same person, use um ... zu. Different people, use damit with the verb at the end. Note that damit also works when the subjects match, but it sounds heavier there, so Germans default to um ... zu.

The same test governs ohne ... zu and statt ... zu: Er verließ das Haus, ohne die Tür zu schließen (he did both) versus Er verließ das Haus, ohne dass jemand ihn sah (two different subjects). And do not add a nicht to ohne ... zu - the negation is already inside the ohne. Ohne etwas zu sagen means without saying anything.

Four errors that survive into B2

• Using um ... zu for every zu-infinitive. Ich habe vergessen, um dich anzurufen is wrong. Um only ever means purpose. If you cannot put in order to in the English translation, drop it: Ich habe vergessen, dich anzurufen.
• Splitting the separable verb. zu aufstehen, auf zu stehen - both wrong. One word: aufzustehen.
• English -ing after a preposition. German has no gerund. Instead of working is statt zu arbeiten, and for learning German is often zum Deutschlernen, not für Deutsch lernen.
• Forgetting that um ... zu answers wozu, not warum. Warum usually wants weil. Ich lerne Deutsch, weil ich in Berlin lebe explains a cause; um in Berlin zu arbeiten states a goal. Mixing them makes sentences sound off even when the syntax is clean.

If you want the full syntactic account with every exception, a printed reference grammar - Hammer's German Grammar and Usage is the standard - will beat any app chapter, including ours. Buy it, keep it on the shelf, consult it twice a year. What a reference book cannot do is make the pattern automatic under time pressure, and that is the actual bottleneck for most learners.

Make it automatic, not just understood

You will understand this page in ten minutes. Producing um dich rechtzeitig anzurufen in real speech, without a pause, takes a few hundred repetitions spread over weeks. That is exactly what spaced repetition is for: the grammar library explains the pattern, the decks drill it inside full sentences with native audio, and the review schedule brings each structure back just before you would have lost it. Vocabulary you meet in those sentences links straight to /vocab, so the grammar and the words reinforce each other instead of competing.

Start with twenty sentences containing separable verbs after zu, and twenty pairs that force the um ... zu versus damit choice. Two weeks of five-minute reviews and you will stop thinking about it. See pricing if you want the whole A1-C2 path on that schedule.