Following Chomsky's theory,
the passive fails to assign Case to the internal argument
A barrier is inserted which blocks government.
The idea behind this is that the internal
argument is marked as prominent.
NPs marked as prominent ([+Prom]) are
to be raised to the subject position.
NPs in the subject position are assigned
the nominative Case ([+Nom]).
A general principle will state that NPs
cannot be assigned two different Cases.
The internal argument would be marked
for both [-Nom] (form the verb) and [+Nom].
The barrier blocks Case assignment in
the passive, so that only Case will be assigned to the internal
argument.
PromP
Prominence (Prom)
Traditionally called the subject, it
marks one of certain NPs as prominent, but it is not related
to focus (new information) in English) or preposing (old information).
It targets either the internal argument
(active voice) or the external argument (passive voice).
VP --> V1 + PP
V1 --> V0 + NP.
or
VP --> V2 + PP
V2 --> V1 + NP.
V1 --> V0 + NP
[+Prom]
PT (Phrase-Target) is the feature of
the target: [±PT]
The targeted NP is prominent.
The features of the targeted prominent
NP are copied to the subject position ([+Prom]).