Syntactic Theory
Passive
The Verb Be in Passive Sentences
In passive sentences, the passive participle is usually preceded by a form of be, as shown in (1). However, examples (2)-(4) show that passive participles can also occur in environments that lack any form of be (examples taken from Sag, Wasow, Bender 2003, p.319).
- The article was written (by Chomsky).
- The cat got bitten (by the dog).
- Liked by many people but respected by few, Jean will have to run an aggressive reelection campaign.
- Anyone handed a note will be watched closely.
Hence, the property that passive participles are typically preceded by a form of be is not built into the Passive Lexical Rule that produces the passive form of verbs. Rather, a lexical entry for be is introduced that requires to combine with a passive participle.

Pause for a moment and think about what an analysis of the relevant lexical entry for be as it occurs in passive sentences must look like.
An analysis of the lexical entry of passive be needs to provide the following:
Passive be combines with a passive participle. More specifically, passive be takes as complement a verb phrase (VP) whose head daughter, the verb (V), is a passive participle.
Passive participles are generated by the Passive Lexical Rule. In order to be identifiable as a passive participle, the rule says that passive verbs are constrained to be [FORM pass] (cf. the Passive Lexical Rule). Since FORM is a head feature, the verb's FORM feature will also show up on its mother VP node according to the Head Feature Principle.
So, if the lexical entry of passive be is constrained to select a VP[FORM pass] complement, it is guaranteed that the complement's head daughter will be a V[FORM pass].
The next question is: what is the subject (i.e. the value of SPR) of passive be? Consider the following sentences:

- The dog was bitten by the flea.
- *The dog were bitten by the flea.
The agreement indicates that the dog should be treated as the subject (i.e. the SPR) of was. However, in the discussion of passive participles in the previous sections (cf. Introduction, Properties of the Active - Passive Relation, and The Passive Lexical Rule), it was discussed that the dog is the subject of bitten. This was mainly for semantic reasons (to maintain the semantic roles, i.e. that the dog functions semantically as the thing being bitten).
In the analysis of passive be, the subject of be is identified with the subject of the passive verb. This means that there is only one subject NP, and it appears as the first element of the ARG-ST list of both be and the passive verb. As the subject of be it satisfies the agreement constraints required by the inflected form of be. As the subject of the passive verb, it is assigned the correct semantic role, namely the semantic role that the object would have in an active sentence (the BITTEN role, rather than the BITER role).
In order to identify the subject of be with the subject of the passive verb, a constraint is added which specifies that the first argument of be (the first element on its ARG-ST list, its subject) is identical to the SPR value of its complement, the VP[FORM pass] argument. This is accomplished through the device of tagging. Due to the Valence Principle, the SPR value of the VP is also identical to the SPR value (the subject) of its head daughter, the passive verb.
So, the lexical entry for passive be can be formulated as follows:
Lexical Entry of Passive Be

from Sag/Wasow/Bender 2003, p. 320
It satisfies all the requirements mentioned above. In addition, it ensures that the auxiliary be makes no semantic contribution except that its INDEX value is identified with that of its complement.