What's good to know
The Zustandspassiv (=passive of state) sounds way more complicated than it actually is. While it might be intellectually satisfying to understand why "Der Pastor ist verheiratet." is not the Perfekt tense - that would be "Der Pastor hat (seine Tochter) verheiratet." it is also completely unnecessary to do so thanks to its similarity with English and many other languages. Take a look at the following sentences:
A: Das Auto ist gewaschen. - The car is washed. === ZUSTANDSPASSIV
B: Das Auto wird gewaschen. - The car is being washed. === VORGANGSPASSIV (STANDARD PASSIVE)
C: Das Auto ist gewaschen worden. - The car has been washed. === PASSIV PERFEKT
If you look at the translation of A, you'll notice that the sentence structure is exactly the same as in English. That means you don't have to understand anything in regard of logic. Knowing your vocabulary will actually do the job.
A bit more complicated approach: If you feel already comfortable with C, all you got to do to get to A is to cut out the "worden". Not too difficult right?
Two more examples in slightly changed order:
D: Das Essen wird gekocht. - The food is being cooked. === VORGANGSPASSIV
E: Das Essen ist gekocht worden. - The food has been cooked. === PASSIV PERFEKT
F: Das Essen ist gekocht. - The food is cooked. === ZUSTANDSPASSIV
G: Die Kinder werden versorgt. - The kids are being taken care of.
H: Die Kinder sind versorgt worden. - The kids have been taken care of.
I: Die Kinder sind versorgt. - The kids are taken care of.
How to differentiate between the Perfekt mit sein and the Zustandspassiv?
Should you ever find yourself asking whether you got the Perfekt or the Zustandspassiv in front of you, you'll have to know your verbs that build the Perfekt tense with sein. E.g. in...
J: Der Gast ist gekommen. - The guest is or has arrived?
"kommen" is as you hopefully already know a verb that builds the Perfekt with sein. As those verbs can't build any kind of passive form, the answer whether we have a Perfekt or a Passive here is clear.
Verbs for which there's no passive
There are other verbs that don't have a passive form but instead of learning those by heart from a random list, dive a bit deeper into the logic of the passive and those verbs. "kommen" is an activity that requires you to be active. You can't be made "come". That would mean that your legs would move without your brain steering them. That's not really possible or lets say highly unusual.
Can you figure out why the following verbs can't build a passive form?
- sich erkälten (or any other reflexive verb) - to get a cold
- aufstehen - to get up
- lügen - to lie
- frieren - to be cold
- können (and all other modal verbs) - to be able to
- es gibt - there is/are
- kosten - to cost
- wissen & kennen - to know
This topic is covered in: C1-L14