Form and function: Subject and Predicat, Characteristics of subject, Realisations of subject
We have used the word "form" quite often in the Internet Grammar. It was one of the criteria we used to distinguish between word classes -- we saw that the form or "shape" of a word is often a good clue to its word class.
When we looked at phrases, too, we were concerned with their form. We said that phrases may have the basic form (Pre-Head string) - Head - (Post-Head string).
And finally, we classified clauses according to the form (finite or nonfinite) of their main verb.
In all of these cases, we were conducting a FORMAL analysis. Form denotes how something looks -- its shape or appearance, and what its structure is. When we say that the old man is an NP, or that the old man bought a newspaper is a finite clause, we are carrying out a formal analysis.
We can also look at constituents -- phrases and clauses -- from another angle. We can examine the FUNCTIONs which they perform in the larger structures which contain them.
The most familiar grammatical function is the SUBJECT. In notional terms, we can think of the Subject as the element which performs the "action" denoted by the verb:
 David plays the piano
 The police interviewed all the witnesses
In , the Subject David performs the action of playing the piano. In , the Subject the police performs the action of interviewing all the witnesses. In these terms, this means that we can identify the Subject by asking a wh-question:
 David plays the piano
Q. Who plays the piano?
A. David ( = Subject)
 The police interviewed all the witnesses
Q. Who interviewed all the witnesses?
A. The police (= Subject)
Having identified the Subject, we can see that the remainder of the sentence tells us what the Subject does or did. In , for example, plays the piano tells us what David does. We refer to this string as the PREDICATE of the sentence. In , the Predicate is interviewed all the witnesses.
Here are some more examples of sentences labelled for Subject and Predicate.
enjoys going to the cinema
The girl in the blue dress
In each of these examples, the Subject performs the action described in the Predicate. We've seen, however, that there are problems in defining verbs as "action" words, and for the same reasons, there are problems in defining the Subject as the "performer" of the action. The Subject in John seems unhappy is John, but we would hardly say he is performing an action. For this reason, we need to define the Subject more precisely than this. We will look at the characteristics of the Subject on the next page.
The grammatical Subject has a number of characteristics which we will examine here.
1. Subject-Verb Inversion
In a declarative sentence, the Subject comes before the verb:
Declarative: David is unwell
When we change this into a yes/no interrogative, the Subject and the verb change places with each other:
If an auxiliary verb is present, however, the Subject changes places with the auxiliary:
Declarative: Jim has left already
Interrogative: Has Jim left already?
In this interrogative, the Subject still comes before the main verb, but after the auxiliary. This is true also of interrogatives with a do-auxiliary:
Declarative: Jim left early
Interrogative: Did Jim leave early?
Subject-verb inversion is probably the most reliable method of identifying the Subject of a sentence.
2. Position of the Subject
In a declarative sentence, the Subject is usually the first constituent:
Jim was in bed
Paul arrived too late for the party
The Mayor of New York attended the banquet
We made a donation to charity
However, there are exceptions to this. For instance:
Yesterday the theatre was closed
Here, the first constituent is the adverb phrase yesterday, but this is not the Subject of the sentence. Notice that the theatre, and not yesterday, inverts with the verb in the interrogative:
Declarative: Yesterday the theatre was closed
Interrogative: Yesterday was the theatre closed?
So the Subject here is the theatre, even though it is not the first constituent in the sentence.
3. Subject-verb Agreement
Subject-verb AGREEMENT or CONCORD relates to number agreement (singular or plural) between the Subject and the verb which follows it:
Singular Subject: The dog howls all night
Plural Subject: The dogs howl all night
There are two important limitations to Subject-verb agreement. Firstly, agreement only applies when the verb is in the present tense. In the past tense, there is no overt agreement between the Subject and the verb:
The dog howled all night
The dogs howled all night
And secondly, agreement applies only to third person Subjects. There is no distinction, for example, between a first person singular Subject and a first person plural Subject:
I howl all night
We howl all night
The concept of NOTIONAL AGREEMENT sometimes comes into play:
The government is considering the proposal
The government are considering the proposal
Here, the form of the verb is not determined by the form of the Subject. Instead, it is determined by how we interpret the Subject. In the government is..., the Subject is interpreted as a unit, requiring a singular form of the verb. In the government are..., the Subject is interpreted as having a plural meaning, since it relates to a collection of individual people. Accordingly, the verb has the plural form are.
4. Subjective Pronouns
The pronouns I, he/she/it, we, they, always function as Subjects, in contrast with me, him/her, us, them:
I left early
*Me left early
He left early
*Him left early
We left early
*Us left early
They left early
*Them left early
The pronoun you can also be a Subject:
You left early
but it does not always perform this function. In the following example, the Subject is Tom, not you:
Tom likes you
In the sentence, Jim was in bed, the Subject is the NP Jim. More precisely, we say that the Subject is realised by the NP Jim. Conversely, the NP Jim is the realisation of the Subject in this sentence. Remember that NP is a formal term, while Subject is a functional term:
Subjects are typically realised by NPs. This includes NPs which have pronouns , cardinal numerals , and ordinal numerals  as their Head word:
 [We] decided to have a party
 [One of my contacts lenses] fell on the floor
 [The first car to reach Brighton] is the winner
However, other constituents can also function as Subjects, and we will examine these in the following sections.
Clauses functioning as Subject
Clauses can also function as Subjects. When they perform this function, we refer to them generally as Subject clauses. The table below shows examples of the major types of Subject clauses:
Nominal Relative clause
 That his theory was flawed soon became obvious
 What I need is a long holiday
 To become an opera singer takes years of training
 Being the chairman is a huge responsibility
Notice that some of these Subject clauses have Subjects of their own. In , the Subject clause that his theory was flawed, has its own Subject, his theory. Similarly, in , the Subject of what I need is I.
Among nonfinite clauses, only to-infinitive clauses and -ing participle clauses can function as Subject. Bare infinitive clauses and -ed participle clauses cannot perform this function. In the examples above --  and  -- the nonfinite Subject clauses do not have Subjects of their own, although they can do:
[3a] For Mary to become an opera singer would take years of training
[4a] David being the chairman has meant more work for all of us
Prepositional Phrases functioning as Subject
Less commonly, the Subject may be realised by a prepositional phrase:
After nine is a good time to ring
Prepositional phrases as Subject typically refer to time or to space.