In the passive voice, the focus is on what is happening to the subject. However, you can still mention who performed the action by using the preposition door (by).
Expressing the Agent with door
To add the agent (the "doer") to a passive sentence, simply place door followed by the person or thing performing the action. The grammar rules for the passive voice do not change: the conjugated auxiliary verb (like worden) stays in the second position, and the past participle is pushed to the end of the clause.
| The novel is read by the writer. | De roman wordt door de schrijver gelezen. |
| Is this book published by the publisher? | Wordt dit boek door de uitgever uitgegeven? |
Perfect Tenses and Modal Verbs
You can use door in any tense. If a passive sentence uses the perfect tense (with zijn) or a modal verb (like moeten), the door phrase simply sits in the middle of the sentence, framed by the verbs.
| The first chapter is written by the poet. | Het eerste hoofdstuk is door de dichter geschreven. |
| The book must be published by a publisher. | Het boek moet door een uitgever worden uitgegeven. |
| The chapters must be translated by the translator. | De hoofdstukken moeten door de vertaler worden vertaald. |
Passive Relative Clauses
When you use a relative clause to give more information about a noun (e.g., "the novel that is translated"), standard subordinate clause word order applies. All verbs are pushed to the end of the clause, and the door phrase sits right before them.
| The novel that is translated by the poet, is beautiful. | De roman die door de dichter wordt vertaald, is mooi. |
| The novels that are written by that famous writer, are expensive. | De romans die door die bekende schrijver worden geschreven, zijn duur. |