Passive with Modal Verbs in German (muss gemacht werden)

German builds the passive with a modal verb by stacking three pieces: the modal verb (conjugated for the subject), the Partizip II of the main verb, and the infinitive werden at the very end of the clause. The pattern is Modalverb … Partizip II + werden, for example Das Formular muss heute ausgefüllt werden ("The form has to be filled in today"). The two non-finite verbs lock together at the end, with the past participle first and werden last.

This is the process passive (Vorgangspassiv), so the final infinitive is always werden, never sein. Compare Das muss gemacht werden ("it has to be done" — an action) with the static sein-passive, which describes a result rather than an action. Using sein here is the classic mistake.

You will meet this structure constantly in instructions, rules, forms and Amtsdeutsch (official German), where the doer is unimportant: Die Tür kann nicht geöffnet werden, Das Antragsformular muss unterschrieben werden. Any modal works — müssen, können, sollen, dürfen — and only the modal changes its form for person and number.