In the passive voice, the action is the most important thing - NOT the person doing the action. The main question is always: What happened?
When we use the passive voice, the subject of the sentence is NOT the person or thing doing the action. Instead, the subject of the sentence is the person or thing receiving the action. Sometimes the person or thing doing the action is mentioned while other times they are not.
ACTIVE: In active voice, the person doing the action (the subject) is important.
(The acting person is important: who is doing something.)
PASSIVE: In passive voice, the action itself is important.
(The action is important. Who is cooking the soup doesn't matter or is unknown.)
If you still want to mention who did the action, you need to use a preposition + von + dative construction.
In German, there are two types of passive: Process Passive and Status Passive. They have different meanings, constructions, and uses. In the next two lessons I'll show you the difference. I've also included another lesson on the so-called "impersonal passive." Technically it's a type of process passive, but it can cause confusion for students so I gave it its own lesson to explain it in more detail.
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