FUNCTIONS OF THE SENTENCE

We have described the functions of language in terms of segmentation - the ways in which the different units combine to form larger units, and their functioning as elements in clause structure. These are functions which operate within language as a system, but there is another sense too in which grammar is "functional", and this relates to what we actually do with language when we use it to communicate. Morphemes, words, groups and clauses cannot in themselves do this. It is only in so far as they may be constituted to form sentences that they function in communication. We can of course, as we have seen above, have a sentence which consists of a single clause, which may in turn consist of a single group, a single word, and even a single morpheme. But it is only at the level of sentence that we can make statements, responses, requests, ask questions or make comments and exclamations. The sentence is the smallest grammatical unit which can perform such functions. Whenever we perform such functions, as in a dialogue, we adopt particular speech roles for the purpose. For example, in asking a question a speaker takes on the role of seeker of information. A second participant is required to adopt the role of listener and provider of the information sought. The whole event thus takes on the form of an exchange of information, or what may be described as an interaction. Whether in this or any of the many other roles which speakers may adopt in interaction, we are obliged to make the appropriate grammatical choices for whichever role we have assumed. The list of possible speech role / functions is very long, and will include such diverse acts as paying someone a compliment, asking the time, demanding attention orissuing a threat. It is not generally possible to identify specific grammatical forms for each such specific function, although we may be able to note certain characteristics which might be typical of any given class of communicative act. What we can do, however, is to describe the basic system of choices regarding the structural features within the sentence, which relates to how speakers are able to express their various messages and comments, and in terms of which the totality of speaker interaction is carried on. The grammatical system which relates most directly to this broad area of speaker role is called the MOOD SYSTEM. This system is governed by two elements of clause structure, the subject and the predicator. Selection of mood is determined according to two principles:- (a) the presence or absence in the clause of S and P; (b) the order of S and P. (a) A clause which has no predicator is regarded as MOODLESS. A clause which has a predicator in the base form but no subject has selected the IMPERATIVEmood. A clause which contains both S and P has selected  INDICATIVE mood. (b) Where both S and P are present, if the order is SP the clause has chosen DECLARATIVE mood, if PS then it is INTERROGATIVE mood. The basic system network for mood can be represented as follows.
Let us consider first the phenomenon of moodless clauses. These occur commonly in spoken language, exclamations, public announcements, advertising, titles, headings and many miscellaneous utterances which serve a variety of communicative functions. They are essentially context bound in terms of their meaning and function. Here are a few such examples, for which a likely context should be readily apparent.
(1) Good morning.
(2) Any more wine, sir?
(3) Well, just a little more.
(4) Alliance jubilation after election victory.
(5) Good gracious!
(6) Why me?
(7) Good luck and best wishes for a happy new year.
(8) Bargains galore inside!
(9) Rates up 40% in Birmingham.
(10) House prices up 7% in six months.
Where there is a predicator but no subject then the clause has selected imperative mood. There are two main types of imperative, the form which has only an uninflected main verb, and the form with "LET'S". These function differently in that the former is "speaker exclusive", since the activity is required to be performed by the addressee only, whereas the latter is "speaker inclusive" - both speaker and addressee are expected to perform the act.
e.g.	Come on, think. Tell me the answer.
	Let's go now.
The verb is always in its base form (i.e. not inflected). Do not confuse subjects with vocatives. e.g. You boys at the back be quiet. Here "you boys at the back" is a vocative (a form of address), and not a subject; compare with: You boys at the back are quiet. Is anything wrong? Clauses which have both S and P are indicative mood. In the order SP they are declarative, which is the usual form for statements.
e.g.	It's raining.
	The exam was easy.
Clauses which have the PS sequence are interrogative, which is a typical form for questions. There are basically two forms for this:
(i)	P[S] where S is inside P; the predicator consists of two or more words.
	e.g. Does he smoke?
(ii)	PS where S follows P; the predicator consists of one word.
	e.g. Is he a teacher?
This leads us to consider those verbs which we have already alluded to earlier, which are known as OPERATORS. These are BE, DO, HAVE and the various modal auxiliary verbs which combine with an inflected form of the main verb. It is in fact the operator part of the predicate which forms the inversion with the subject, and type (ii) above only involves the operator. These only occur in short ellipted responses, with the exception of BE and HAVE, which can function as main verbs. e.g. Does he? Can you? Is he French? Have they any children? Interrogatives are also subject to a system of POLARITY. That is, there are questions like those quoted above for which there is a simple YES / NO response, and which are called POLAR; and there are other questions which require a different sort of response. e.g. What is your name? When will the train arrive? This latter type are NON-POLAR, and they in turn fall into two categories. There is the type as illustrated above which feature the normal PS inversion, and there is also the form which features a WH- word in S position while the rest of the clause has the normal declarative word order. This would thus seem to be an exception to the normal PS form in interrogative clauses. e.g. Which bag is yours? Who told you that? The system network for interrogative mood can then be represented as follows. This brief discussion of the mood system concludes this introductory unit. later units will go into the various aspects of the grammar in more detail, providing the groundwork for filling in the very large gaps which have necessarily been left out of the description offered here. In future units we shall look in more depth at the structure of groups, and the structure of the sentence. So far we have considered the sentence only as single clauses. We shall go on to look at the way clauses combine to form sentences and may themselves be bound in systems of dependence. Another important system which has so far been left undiscussed here is the system of THEME - the way in which the sentence is structured in terms of sequence, the ordering of the structural parts so as to give particular prominence or attention to certain elements. This will also be discussed in a later unit.