Beyond the everyday zu-infinitive (Ich versuche zu schlafen), German has a small set of infinitive constructions that pack a modal meaning — obligation, possibility, necessity — into a compact, often formal package. Das ist noch zu erledigen means "that still has to be done," with no modal verb in sight. Du hast zu gehorchen means "you must obey," again with no müssen. There is also a way to fold a whole zu-infinitive into a single adjective, and a way to point an infinitive backward in time. These four constructions are hallmarks of polished, written German, and recognizing them is essential for reading anything official, legal, or academic.
sein + zu + infinitive: passive obligation or possibility
sein + zu + infinitive is a one-clause substitute for a passive sentence with a modal. It means the subject has to be or can be done. Crucially, it is passive in sense: the subject is the thing acted upon, not the actor.
Das ist noch zu erledigen.
That still needs to be done. (= das muss noch erledigt werden — passive obligation)
Diese Frage ist leicht zu beantworten.
This question is easy to answer. (= kann leicht beantwortet werden — possibility)
So one form covers two modal readings. Context and adverbs decide:
- With leicht, schwer, kaum, gut, nicht → usually possibility (kann): Das ist nicht zu ändern = "that can't be changed."
- With a bare deadline or instruction tone → usually obligation (muss): Die Rechnung ist bis Freitag zu bezahlen = "the bill is to be paid by Friday."
Die Rechnung ist bis Freitag zu bezahlen.
The bill is to be paid by Friday. (formal/official — obligation)
Der Fehler ist kaum zu übersehen.
The mistake is hard to miss. (possibility, with kaum)
This construction is strongly associated with formal and official register (notices, contracts, instructions). In casual speech you would just use a modal: Das muss ich noch machen.
haben + zu + infinitive: active necessity
haben + zu + infinitive is the active mirror image. Now the subject is the actor, and the meaning is obligation or necessity — close to müssen or sollen.
Du hast zu gehorchen.
You are to obey. / You must obey. (active obligation — note the authoritative, formal tone)
Ich habe heute noch viel zu erledigen.
I still have a lot to take care of today. (everyday necessity — this one is colloquial too)
Der Antrag hat folgende Angaben zu enthalten.
The application must contain the following information. (official register)
Note the difference in tone between the two examples. Du hast zu gehorchen is sharp and authoritarian — a command from someone with power. But Ich habe viel zu tun ("I have a lot to do") is completely ordinary, everyday German. The construction ranges from neutral to stern depending on the verb and context.
The contrast between the two constructions mirrors active vs passive perfectly:
| Construction | Voice | Modal equivalent | Example |
|---|---|---|---|
sein
| passive (subject is acted on) | muss/kann ... werden | Das ist zu reparieren. (must/can be repaired) |
haben
| active (subject is the actor) | muss/soll | Du hast das zu reparieren. (you must repair it) |
Das Formular ist auszufüllen, und du hast es zu unterschreiben.
The form is to be filled out, and you have to sign it. (sein + zu passive, then haben + zu active, side by side)
Notice in auszufüllen that with separable verbs the zu slots between the prefix and the stem: aus·zu·füllen, written as one word.
The gerundive: zu + Partizip I as an attribute
You can collapse a whole sein + zu clause into a single adjective placed before the noun. Take zu, attach it to the present participle (Partizip I, the -end form), and decline it like any attributive adjective. The result is the Gerundivum: it carries the same "to-be-done / can-be-done" passive-modal meaning, now as a pre-noun modifier.
die zu lösende Aufgabe
the task to be solved (= die Aufgabe, die gelöst werden muss)
ein kaum zu überbietendes Angebot
an offer that can hardly be topped
Die noch zu erledigenden Punkte stehen auf der Liste.
The points still to be dealt with are on the list.
Build it in three steps: (1) infinitive lösen → Partizip I lösend; (2) prefix zu- → zu lösend; (3) add the adjective ending the noun's case/gender demand → die zu lösende Aufgabe. This is dense, written German — you will meet it constantly in academic and bureaucratic prose and almost never in conversation, where speakers expand it back into a relative clause: die Aufgabe, die gelöst werden muss.
The perfect infinitive: zu + Partizip + haben/sein
To express that an infinitival action happened before the matrix verb, German uses the perfect infinitive: the past participle followed by zu haben or zu sein. It corresponds to English "to have done."
Er behauptet, es getan zu haben.
He claims to have done it. (the doing precedes the claiming)
Sie freut sich, alles geschafft zu haben.
She's glad to have managed everything.
Ich glaube, ihn schon einmal gesehen zu haben.
I think I've seen him before.
The auxiliary follows the same haben/sein split as the Perfekt: motion and change-of-state verbs take sein.
Er behauptet, pünktlich angekommen zu sein.
He claims to have arrived on time. (ankommen is a sein-verb, so: angekommen zu sein)
The word order is rigid: participle + zu + auxiliary, all at the end. getan zu haben, never zu haben getan or getan haben zu. This trips up English speakers, who place "to" before "have" ("to have done") — German places zu before the auxiliary at the very end of the cluster.
Common Mistakes
❌ Das ist noch zu machen werden.
Incorrect — sein + zu + Infinitiv already carries the passive-modal meaning; don't add werden.
✅ Das ist noch zu machen.
That still needs to be done.
The whole point of sein + zu is that it replaces muss gemacht werden. Adding werden doubles up the passive and is wrong.
❌ Er behauptet, es zu haben getan.
Incorrect — wrong order; the participle comes first, then zu haben.
✅ Er behauptet, es getan zu haben.
He claims to have done it.
English "to have done" puts the marker first; German puts zu haben last, after the participle. Reorder accordingly.
❌ die zu lösend Aufgabe
Incorrect — the gerundive participle is an attributive adjective and must take an ending.
✅ die zu lösende Aufgabe
the task to be solved (with the adjective ending -e)
❌ Der Antrag hat folgende Angaben enthalten.
Incorrect — without zu this reads as a Perfekt ('has contained'); the obligation construction needs zu.
✅ Der Antrag hat folgende Angaben zu enthalten.
The application must contain the following information.
This is a genuine trap: hat ... enthalten without zu is just the present perfect. The single word zu is what turns it into "must contain." Drop it and you change the tense and the meaning.
❌ Er behauptet, angekommen zu haben.
Incorrect — ankommen takes sein, so the perfect infinitive is angekommen zu sein.
✅ Er behauptet, angekommen zu sein.
He claims to have arrived.
Key Takeaways
- sein + zu + Infinitiv = passive obligation/possibility (muss/kann ... werden), strongly formal: Die Rechnung ist zu bezahlen.
- haben + zu + Infinitiv = active necessity (muss/soll), tone ranging from neutral to stern: Du hast zu gehorchen.
- The gerundive (die zu lösende Aufgabe) folds a sein + zu clause into a single declined adjective; the zu gives it a passive-modal meaning that a plain Partizip I lacks.
- The perfect infinitive Partizip + zu haben/sein marks an action prior to the matrix verb: getan zu haben, angekommen zu sein — with the zu-auxiliary at the very end.
- All four are written-register staples with no one-word English match; in speech, Germans expand them into modals and relative clauses.
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Start learning German→Related Topics
- The zu-InfinitiveB1 — When German uses zu + infinitive at the end of a clause, when it doesn't (modals and perception verbs take a bare infinitive), and where zu goes inside separable verbs.
- Impersonal Passive and Alternatives to the PassiveC1 — The agentless impersonal passive (Es wird getanzt) and the constructions German prefers over the passive: man, sich lassen, sein + zu, and -bar adjectives.
- um...zu, ohne...zu, (an)statt...zuB1 — The three infinitive conjunctions for purpose, 'without doing', and 'instead of doing' — and the same-subject rule that forces damit when subjects differ.
- Modal Verbs: OverviewA2 — The six German modal verbs, their shared word order, and the irregular present tense that makes ich and er identical.
- Participles as AdjectivesB1 — How German present participles (-end) and past participles (gemacht) work as attributive adjectives — and why they always decline.
- Advanced Passive ConstructionsC1 — The dative-verb passive with no subject (Mir wurde geholfen), the impersonal passive (Es wurde getanzt), the recipient bekommen/kriegen-passive, and the passive-like sein+zu+Infinitiv and sich lassen — a synthesis of German's full passive system.