Core meaning
把 (bǎ) is a disposal marker. The speaker is doing something deliberate to a specific, known object. The sentence focuses on what happens to that object: the result state or the effect of the action. 被 (bèi) is the passive marker. The grammatical subject is the patient, not the agent. Something is happening to them, often unintentionally or against their will in older usage, though modern Mandarin has loosened this to neutral passive.
Sentence structure
把 construction: Subject + 把 + Object + Verb + other element (result/direction/duration). The verb cannot stand alone; it must carry a result complement (了, 完, 好, 到, 掉, 住, direction verbs 起来/下去) or an aspect marker. 被 construction: Subject (patient) + 被 + (agent) + Verb + other element. The agent is optional in 被. Both structures require the verb to carry a result or aspect; bare verbs sound ungrammatical in both.
我把蛋糕吃完了。／蛋糕被我吃完了。
Wǒ bǎ dàngāo chī wán le. / Dàngāo bèi wǒ chī wán le.
I finished the cake. / The cake was finished by me.
When you must use 把
Use 把 when the verb has a result/directional/duration complement AND you want the object (not the subject) to be the sentence focus. It is the default for actions that change the state of a specific object: 把门打开 (open the door), 把车开到门口 (drive the car to the door), 把书放在桌子上 (put the book on the table). If you drop 把 in these sentences, Chinese speakers will still understand but the utterance sounds less natural.
When you must use 被
Use 被 when you want to foreground the patient, or when you do not know or do not care about the agent. 被 is common in news, reports, and negative outcomes: 他被解雇了 (he was fired), 我的手机被偷了 (my phone was stolen). Traditional grammar rules said 被 requires a negative outcome; contemporary Mandarin has relaxed this for neutral uses, but negative-outcome sentences still feel the most natural.
我的手机被偷了。
Wǒ de shǒujī bèi tōu le.
My phone was stolen.
Common confusion: can you swap them?
In theory, many 把 sentences can be rewritten with 被 by swapping subject and object. In practice, the two are NOT interchangeable because they emphasise different things. 我把咖啡喝完了 emphasises what I did (finished the coffee). 咖啡被我喝完了 emphasises what happened to the coffee (it got finished by me). Use 把 to talk about the action; use 被 to talk about the result on the patient.
Native-speaker instinct
A rule of thumb: if your English sentence would begin with the agent ("I closed..."), default to 把. If it would begin with the patient or use passive voice ("The door was closed..."), use 被. If neither the agent nor the patient matters and you just want to say the action happened, drop both and use a simple SVO: 我关了门 (I closed the door).
Related grammar points
- 把 Construction (把字句)HSK 3
- Passive with 被 (被字句)HSK 3