Normally, subordinate clauses push the conjugated verb to the very end of the sentence. However, there is a major word order exception when using modal verbs in the Perfect tense.
The Perfect tense of a modal verb requires a "double infinitive" structure: a conjugated form of haben followed by the infinitive of the main verb and the infinitive of the modal verb (for example, haben organisieren müssen).
If this double infinitive structure lands in a subordinate clause, the conjugated haben does not go to the very end. Instead, it jumps to the front of the verb cluster, sitting immediately before the two infinitives.
| We are tired because we had to organize the demonstration. | Wir sind müde, weil wir die Demonstration haben organisieren müssen. |
Notice how haben comes directly before organisieren müssen, rather than at the absolute end of the sentence. This rule applies to all subordinate clauses, including those introduced by dass (that):
| The speaker says that the president wanted to approve our demand. | Der Redner sagt, dass der Präsident unsere Forderung hat genehmigen wollen. |
| The speakers are angry because they wanted to speak peacefully. | Die Redner sind wütend, weil sie friedlich haben sprechen wollen. |
Negation
When you need to negate a double infinitive in a subordinate clause, place nicht immediately before the entire three-verb cluster (right in front of haben).
| The crowd is angry because the police did not want to approve the demand. | Die Masse ist wütend, weil die Polizei die Forderung nicht hat genehmigen wollen. |