The Passive is a construction in which the grammatical subject of a verb plays the same semantic role that the object plays when the verb in question appears in active forms. The term 'passive' is used to refer both to this construction, and to the verb whose arguments' roles are at issue.
Consider the following examples:
(1) a. The flea bit the dog. b. The dog was bitten (by the flea). (2) a. Sue sent Mary the letter. b. Mary was sent the letter (by Sue).
The b-sentences are the 'passive' sentences, the a-sentences are their 'active' counterparts. Notice the close semantic relationship between the active and passive sentences. The arguments have the same semantic roles: in (1), the flea is the biter, and the dog is the one being bitten. In (2), Mary is the recipient of the letter, and Sue is the sender.
To find out more about the relationships between Active and Passive, go to the next section, Properties of the Active - Passive Relation.