Bèi (被) and gěi (給) both can serve as passive markers in a sentence to indicate the subject being the recipient of an action. A major difference between these two words is as follows: gěi (給) is used to express the passive voice, both the agent and the theme are required in the sentence, as for bèi (被) sentences, the agent can be omitted. For example, if using bèi (被) and gěi (給) sentences to express the meaning of the fish was eaten, the correct forms should be the following:
魚被(貓)吃了.
yú bèi (māo) chī le.
The fish was eaten (by the cat).
魚給貓吃了。
yú gěi māo chī le.
The fish was eaten by the cat.
It is ungrammatical to express the meaning of the fish was eaten by saying yú gěi chī le (魚給吃了, in this case, the role of yú (魚) needs to change from the theme into the agent to make the expression understandable.
--剛買的那包魚食呢?
gāng mǎi de nà bāo yú shí ne?
where is the pack of fish food we just bought.
--魚給吃了。
yú gěi chī le.
The fish ate it.
Therefore, when gěi (給) is used to indicate the passive voice, the pattern should be:
N1+ gěi (給)+N2+verb phrase
theme agent
The pattern of bèi (被) sentences is:
N1+ bèi (被)+(N2)+verb phrase
theme agent
It should be noted that gěi (給) can also be used it bèi (被) in the passive voice. This structure would be: bèi (被)... gěi (給)…. In this structure, gěi (給) here is used to emphasize the passive voice.
魚被貓給吃了。
yú bèi māo gěi chī le.
The fish was eaten by the cat.
