Someone gets pegged as something they are not, by someone else's judgment.
序 · The move
1Put the one being judged in front as subject.Is this the person the label lands on, not the one doing the judging?
2Mark 被, then name the agent who does the judging (or drop it if unknown).Could a 被-less active sentence with the agent first say the same thing? Then this frame fits.
3Choose the treat-as verb (當作 / 看作 / 視作 / 說成) and place the identity noun after it.Does the tail give an identity the subject is equated to, not an action done to them?
例 · Examples
1他he被passive marker — the one acted upon鄰居the neighbors (the agent)當作treat as, take for小偷a thief (the identity pinned on him)。
Plain 被 has an action done to the subject; 被…V作/做… has an identity assigned to the subject. The tail is a noun they are equated to, not a verb done to them.
active 當作 (我把他當作朋友)
Active 當作 / 把…當作 has the subject doing the judging; 被…當作 flips it — the subject is the one judged. Success: 他被當作小偷 (he is judged). Failure if reversed: 他當作小偷 wrongly makes him the judge.
他被鄰居當作了小偷的人。 → 他被鄰居當作小偷。 (the identity noun ends the clause; no 的人 tail)
鄰居被他當作小偷。 → 他被鄰居當作小偷。 (the one judged is the subject, the judge follows 被)
他被當小偷。 → 他被當作小偷。 (the treat-as sense needs 作/做 after the verb, not 當 alone)
English "treated as / taken for" puts the judged person up front and that maps onto 被…V作/做…; the trap is reaching for plain 被 + verb and losing 作/做, which is what carries the "as" equation.