CRITERIA FOR THE CLASSIFICATION OF CLAUSE ELEMENTS
Ability to become the subject
Objects can normally become the subject in a passive clause, since the system of voice allows different semantic roles to be associated with Subject and Object functions (The bomb killed the policeman/The policeman was killed by the bomb; I sent her an email/She was sent an email).
However, passivization with ‘promotion’ to subject is not a watertight criterion for the identification of object functions. It can be too exclusive and too inclusive. Passivization excludes from object status NGs following verbs such as fit, which otherwise fulfil the criteria for objects.
Conversely, passivization can promote to subject NGs that are not objects. Such is the case in the well-known example This bed was slept in by Queen Victoria, derived from the active Queen Victoria slept in this bed, in which this bed is part of a prepositional phrase (PP) functioning as a locative Complement, not as an object. A prepositional phrase has within it a nominal group, however, which increasingly in present-day English is able to become subject in a corresponding passive clause. Examples of this kind, such as The flowerbeds have been trampled on occur when the subject referent is visibly affected by the action, as is the case of the flowerbeds, or acquires some importance, as in the case of the bed slept in by Queen Victoria.
