lassen + Infinitiv: have something done, let somebody do it, sich lassen

Rule

lassen does two jobs. Alone it is a full verb meaning leave something somewhere or stop doing something. With a second verb in the bare infinitive it means have something done or let somebody do something — and there it behaves like a modal verb: no zu, and the infinitive closes the sentence bracket.

Three readings of lassen + Infinitiv:

• Causative — you have it done. Somebody else does the work: Wir lassen das Auto reparieren. The person doing it can be named in the accusative (Ich lasse den Klempner kommen). If the job is done for the subject and the thing affected is already the accusative object, the beneficiary is dative: Ich lasse mir die Haare schneiden.
• Permissive — you allow it. Sie lässt ihn ausreden; the person allowed stands in the accusative.
• sich lassen + Infinitiv — it is possible. Das lässt sich reparieren = Das kann repariert werden. This is one of the everyday alternatives to a passive with können; adverbs such as leicht, gut or kaum and a negation are frequent but not required.

Forms. lassen is a strong verb with a → ä in the du and er form (du lässt, er lässt), Präteritum ließ. Crucially it has two forms in the Perfekt: the participle gelassen when lassen stands alone, and the Ersatzinfinitiv lassen when a second infinitive follows — Ich habe das Auto reparieren lassen.

Word order. Main clause: lassen in position 2, the infinitives at the end. Subordinate clause in a simple tense: the finite lassen moves to the very end (…, weil ich das Auto reparieren lasse). Subordinate clause with the double infinitive: the finite haben stands in front of both infinitives (…, weil ich das Auto habe reparieren lassen). One more everyday use: Lass uns …! / Lasst uns …! is an invitation — "let's …".

Examples

• Ich lasse den Schlüssel zu Hause. — I'm leaving the key at home.
• Lass mich! — Leave me alone!
• Wir lassen das Auto morgen reparieren. — We're having the car repaired tomorrow.
• Ich lasse mir die Haare schneiden. — I'm getting my hair cut.
• Der Chef lässt den Praktikanten den Bericht schreiben. — The boss has the intern write the report.
• Sie lässt ihn ausreden. — She lets him finish what he is saying.
• Meine Eltern lassen mich nicht allein verreisen. — My parents don't let me travel on my own.
• Das Fenster lässt sich nicht öffnen. — The window can't be opened.
• Ich habe das Auto reparieren lassen. — I had the car repaired.
• Ich weiß nicht, warum sie den Vertrag nicht hat prüfen lassen. — I don't know why she didn't have the contract checked.
• Lass uns morgen ins Kino gehen! — Let's go to the cinema tomorrow!

Quick table

Imperative: Lass! – Lasst! – Lassen Sie! · Perfekt: hat gelassen on its own, hat … lassen with a second infinitive.

Common mistakes

• ❌ Ich habe das Auto reparieren gelassen. → ✅ Ich habe das Auto reparieren lassen. — with a second infinitive lassen forms the Ersatzinfinitiv; gelassen only works when lassen stands alone.
• ❌ Ich lasse mein Auto zu reparieren. → ✅ Ich lasse mein Auto reparieren. — like a modal verb, lassen takes the bare infinitive without zu.
• ❌ Das Fenster lässt nicht öffnen. → ✅ Das Fenster lässt sich nicht öffnen. — the possibility reading needs the reflexive pronoun sich.
• ❌ …, weil ich das Auto reparieren lassen habe. → ✅ …, weil ich das Auto habe reparieren lassen. — in a subordinate clause with a double infinitive the finite verb goes in front of both infinitives.
• ❌ Ich lasse mich die Haare schneiden. → ✅ Ich lasse mir die Haare schneiden. — die Haare is already the accusative object, so the person it is done for goes into the dative.

Related

The double infinitive works exactly as with the modal verbs. For Das lässt sich reparieren, compare the passive with können; if you keep adding zu, the chapter on the infinitive with zu shows which verbs need it.