When you want to use a modal verb (like moeten, willen, or kunnen) together with another verb in the perfect tense, Dutch does something unique. Instead of using a past participle for the modal verb, it reverts to its infinitive form.
Because the main verb is also in its infinitive form, this rule creates a "double infinitive" at the end of the sentence. Grammatically, this is known as the infinitivus pro participio (infinitive instead of participle) rule.
| Subject | Auxiliary | Rest of sentence | Modal Infinitive | Main Infinitive |
|---|---|---|---|---|
| Wij | hebben | bij de grens op de douane | moeten | wachten. |
| We have had to wait for customs at the border. | Wij hebben bij de grens op de douane moeten wachten. |
Word Order at Customs
Just like in a standard perfect tense sentence, the conjugated auxiliary verb (hebben) sits in the second position of a main clause. The two infinitives are pushed all the way to the end. The modal verb almost always comes right before the main verb.
| I have had to show my luggage to customs. | Ik heb mijn bagage aan de douane moeten tonen. |
In a question, the auxiliary verb moves to the front (or immediately follows the question word), but the double infinitives stay firmly at the end.
| Why has he had to show a valid visa at the border? | Waarom heeft hij een geldig visum bij de grens moeten tonen? |
Separable Verbs and Other Modals
If the main verb at the end of the sentence is a separable verb, such as aangeven (to declare), it does not split apart. It stays as one complete infinitive word.
| What have you had to declare at the checkpoint? | Wat heb jij bij de controle moeten aangeven? |
This double infinitive rule applies to all modal verbs, not just moeten. You will construct the exact same pattern with verbs like kunnen (to be able to) or willen (to want to).
| Has customs been able to find the perpetrator who wants to smuggle the gold? | Heeft de douane de dader kunnen vinden die het goud wil smokkelen? |
