Syntactic roles refer to the functions that words or phrases play in a sentence. They are concerned with the grammatical structure. On the other hand, semantic roles refer to the functions that words or phrases play in relation to the meanings of verbs. They are concerned with the roles played by different participants in an action or event. In a passive sentence, the syntactic roles are different from the semantic roles. The subject of the passive sentence (syntactic role) becomes the one undergoing the action (semantic role), while the object of the passive sentence (syntactic role) becomes the one performing the action (semantic role).