When a modal verb appears in a perfect tense construction — expressing “could have,” “must have,” “wanted to have” — Dutch uses a double infinitive instead of a past participle of the modal. This is one of Dutch’s most distinctive grammatical features. Instead of “hij heeft gemoeten”, Dutch says “hij heeft moeten werken” (he has had to work) — both the modal and the main verb appear in the infinitive form.
The double infinitive rule applies to all six modal verbs: kunnen → heeft kunnen, moeten → heeft moeten, willen → heeft willen, mogen → heeft mogen, zullen → heeft zullen, hoeven → heeft hoeven te. In subordinate clauses, the double infinitive clusters at the end: “…omdat hij heeft moeten werken” (because he has had to work). The auxiliary heeft comes before the two infinitives. Some speakers and regions prefer the auxiliary at the very end: “…omdat hij moeten werken heeft” — both orders exist.
The double infinitive also appears with perception verbs (zien, horen, voelen) and causative verbs (laten, helpen): “Ik heb hem zien lopen” (I saw him walking), “Ze heeft hem laten gaan” (She let him go). Recognizing these double infinitive constructions in subordinate clauses — where all the verbs cluster at the end — is essential for reading complex Dutch sentences without getting lost in the verb cluster.