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There are two main types of empty categories in the theory of grammar: trace and pro. A trace is an empty category caused by movement, which occurs when a constituent is moved to another position in a phrase marker. On the other hand, pro is a base-generated empty NP that remains empty at S-structure. Pro is an empty category that relates to an antecedent NP (a matrix subject) in a sentence.
Empty INFL
We will begin our discussion of empty categories by examining the following pair of sentences from American Vernacular English (as provided by Radford, et al, 1999:304):
1. (a) I’m playing baseball.
(b) We/You/They playing baseball.
Example (1a) contains an overt form of the auxiliary "be," namely, the contracted form "’m." However, the examples in (1b) contain no overt form of "be." Yet, there are good reasons to suppose that they contain a covert/null or empty variant of "are/is," which we will symbolize as ∅. If this is so, (1a) and (1b) will have essentially the same underlying structure as (2a) and (2b):
2. IP
PRN
I
I
VP
N
V
(a) I’m playing baseball.
(b) We playing baseball.
Since (2b) is an IP headed by a null variant (∅) of "are," we can provide a straightforward account of why the subject "we" is nominative (because ∅ is a variant of the auxiliary "are," and it requires a nominative subject), and why the complement verb "playing" is in the "-ing" form (because ∅ is a variant of "are," and it requires a complement feature of the auxiliary "are" that selects a complement headed by a verb in the "-ing" form).
Further evidence that structures like (2b) contain a null auxiliary comes from examples involving "have" reported by Ralph Fasold, such as the following (where "gonna" = "going to"):
3. He gonna be there, I know he is.
In structures like (3), the italicized auxiliary in the second clause is a copy of the one in the first clause in some other varieties of English. The following examples illustrate this point:
4. (a) He can do it, I know he can.
(b) She is crying, I know she is.
(c) They will kill it, I know they will.
So, the fact that the auxiliary appears in the second clause suggests that the first clause contains a null counterpart.
Although standard varieties of English do not allow the use of a null auxiliary in sentences like (1), there are specific types of constructions in which auxiliaries can be null. In this connection, consider the sentences in (5):
5. (a) He was eating and she was drinking.
(b) He was eating and she – drinking.
Sentence (5b) seems to contain a gap in the position marked "-." The auxiliary "was" has been omitted in (5b) to avoid repetition, and we say that it has undergone a particular kind of ellipsis known as gapping, resulting in the structure in (6) below:
6. IP
PRN
I
she
I
V
drinking
As can be seen in (6), the clause is an IP headed by a null auxiliary, ∅. If we assume that ∅ here is a null variant of "was," we can account for the fact that the subject is "she" (since "was" requires a third person singular nominative subject like "he" or "she"), and the verb "drinking" is in the progressive "-ing" form (since "is" requires a complement headed by a verb in this form).
Pro: The Empty Subject of Infinitive Clauses
Compare the structure of the bracketed infinitive clauses in (7a) and (7b):
7. (a) I would like [you to sleep].
(b) I would like [to sleep].
Each of the bracketed infinitive clauses in (7) is an IP headed by the infinitive particle "to," and each bracketed IP serves as the complement of the verb "like," and therefore a complement clause. An apparent difference between the two is that the bracketed infinitive clause in (7a) has an overt subject, "you," whereas its counterpart in (7b) appears to be subjectless. However, it is evident that the apparently subjectless infinitive clauses contain understood null subjects. Since the null subject found in infinitive clauses has much the same grammatical properties as pronouns, it is conventionally understood as "PRO."
Given this argument, sentence pairs such as (7a) and (7b) have essentially the same structure except that the bracketed IP has an overt pronoun "you" as its subject in (7a), but a covert PRO as its subject in (7b). These structures can be represented as (8a) and (8b) below:
8. IP
PRN I
I VP
V IP
PRN I
I V
(a) I would like you to sleep.
(b) I would like PRO to sleep.
Introducing the relevant technical term, we can say that the null subject PRO in (8b) is controlled (that is, refers back to) the subject "I" of the "would" clause, or equivalently, that "I" (i.e., the expression which PRO refers back to) is the controller or antecedent of PRO. Verbs such as "like," which allow an infinitive complement with a PRO subject, are said to function as control verbs.
An obvious question to ask at this point is why we should agree that apparent subjectless infinitive complements like those bracketed in (7b) have a null PRO subject. Part of the motivation for positing PRO is semantic in nature. In traditional grammar, it is claimed that subjectless infinitive clauses have an understood or implicit subject, and positing a PRO subject in such clauses is one way of capturing the relevant intuition. The implicit subject becomes explicit if the relevant clauses are paraphrased by a clause containing an auxiliary like "will," as in the paraphrase of (9a) given in (9b):
9. (a) The lecturer hopes [to be understood].
(b) The lecturer hopes [he will be understood].
The fact that the bracketed clause in (9b) contains an overt (underline) subject makes it plausible to suppose that the bracketed clause in (9a) has a covert PRO subject.
There is also syntactic evidence in support of the claim that subjectless infinitive clauses have covert PRO subjects. Part of this evidence comes from the syntax of reflexives (i.e., "-self/-selves" forms such as "myself," "yourself," "himself," "themselves," etc.). As can be observed in the following examples, a reflexive generally requires a local (i.e., nearby) antecedent:
10. (a) They want [John to help himself].
(b) *They want [John to help themselves].
In examples like (10), a local antecedent means an expression to which the reflexive can refer back within the same (bracketed) clause. Thus, (10a) is grammatical because it satisfies this locality requirement: the antecedent of the reflexive "himself" is the noun "John," and "John" is contained within the same bracketed "help"-clause as "himself." Conversely, (10b) is ungrammatical because the reflexive "themselves" does not have a local antecedent (i.e., it does not have any expression it can refer back to within the bracketed clause containing it); its antecedent is the pronoun "they," and "they" is part of the "want"-clause, not part of the bracketed "help"-clause. In light of this locality requirement, let us consider the example in (11):
11. Kola likes [to praise himself].
We can account for the grammaticality of (11) thus. Given that a reflexive needs a local antecedent, the reflexive "himself" must have an antecedent within its own (bracketed) clause. This requirement will be satisfied if we assume that the bracketed complement clause has a PRO subject as in (12):
12. Kola likes [PRO to praise himself].
We can then say that "himself" has an antecedent within the bracketed clause containing it, since "himself" refers back to PRO. Because PRO in turn refers to "Kola," this means that "himself" refers to the same person as "Kola."
From the foregoing, we can affirm that clauses are IP structures of the form subject + INFL + complement: the subject is an overt or covert pronoun or nominal (i.e., noun-containing) expression, INFL is occupied by an overt or covert auxiliary or infinitive particle, and the complement is a verb or verb phrase.
Extraction-Motivated Empty Categories
Empty categories may occur as a result of gaps resulting from extraction. Let us consider the following examples:
13. (a) Who did Njide see in the office?
(b) Who saw Kunle in the market?
(c) Who did you say you saw in the market?
We will show in (14) that some WH-phrase, originally in situ, moving from an extraction site and landing in [SPEC, CP], leaves gaps at the extraction site:
14. CP
WH- C1
C
IP
NP I1
I VP
[ei] V1
V1 PP
V NP
P1
+WH P NP
D N1
N
who did you see [t] in the church
The gap may be deeper down in the construction as in (13c), reproduced here as (15):
15. Who did you say [CP you saw – in the church]
The WH-phrase, CP-initial in (15), originated from the bracketed clause. This implies that it has crossed two sentence boundaries. Considering that (16c) below is the S-structure of the D-structure (16b) for which (16a) is the surface phonetic form, it becomes obvious that such movements as exemplified above leave traces at the extraction sites.
16. (a) The doctor was arrested.
(b) NPe TNs BE-EN arrest the doctor.
(c) The doctor; was arrested [ti]
Covert Complements
Just as both INFL and its subject can be covert, so too the complement of INFL can be covert in structures where it undergoes ellipsis. For example, in (17) below, B’s reply is understood as an elliptical form of "they may come":
17. A: Do you think they will come?
B: They may.
On the basis of the above, we may suggest that the auxiliary "may" has a null complement, and that the sentence "they may" has the structure shown in (18):
18. IP
PRN T
I V
They may
In (18), "may" is understood as having the same grammatical and semantic features as "come," differing from "come" only in that it has no phonetic features. Thus, clauses are always IP’s of the form: subject + INFL + complement, and the subject may be overt or covert; INFL may be overt or covert; and the complement may be overt or covert.
CONCLUSION
In this unit, we have discussed four kinds of empty categories: empty INFL, Pro, Extraction-motivated, and covert complements. In all of them, we have tried to show that syntactic structures can contain empty constituents. We have also provided arguments in support of this stand. We hope you followed the argument in the discussion. Try to familiarize yourself with the technical terms used in the discussion.
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