Grammar deals with the rules for combining words into larger units. The largest unit that is described in grammar is normally the sentence. However, defining a ‘sentence’ is notoriously difficult, for the reasons we’ll now discuss.
It is sometimes said that a sentence expresses a complete thought. This is a notional definition: it defines a term by the notion or idea it conveys. The difficulty with this definition lies in fixing what is meant by a ‘complete thought’. There are notices, for example, that seem to be complete in themselves but are not generally regarded as sentences: Exit, Danger, 50 mph speed limit.
On the other hand, there are sentences that clearly consist of more than one thought. Here is one relatively simple example:
This week marks the 300th anniversary of the publication of Sir Isaac Newton’s Philosophiae Naturalis Principia Mathematica, a fundamental work for the whole of modern science and a key influence on the philosophy of the European Enlightenment.
How many ‘complete thoughts’ are there in this sentence? We should at least recognize that the part after the comma introduces two additional points about Newton’s book: (1) that it is a fundamental work for the whole of modern science, and (2) that it was a key influence on the philosophy of the European Enlightenment. Yet this example would be acknowledged by all as a single sentence, and it is written as a single sentence.
We can try another approach by defining a sentence as a string of words beginning with a capital (upper case) letter and ending with a full stop (period). This is a formal definition: it defines a term by the form or shape of what the term refers to. We can at once see that as it stands this definition is inadequate, since (1) many sentences end with a question mark or an exclamation mark, and (2) capital letters are used for names, and full stops are often used in abbreviations. Even if we amend the definition to take account of these objections, we still find strings of words in newspaper headlines, titles, and notices that everyone would recognize as sentences even though they do not end with a full stop, a question mark, or an exclamation mark:
Trees May Be a Source of Pollution
An Irish Airman Foresees his Death (title of poem)
Do not enter
But the most serious objection is that the definition is directed only towards orthographic sentences; that is, sentences that appear in the written language. Spoken sentences, of course, do not have capital letters and full stops.
It is in fact far more difficult to determine the limits of sentences in natural conversation, to say where sentences begin and end. That is so partly because people may change direction as they speak and partly because they tend to make heavy use of connectors such as and, but, so, and then. Here is a typical example of a speaker who strings sentences together with and. The symbol <,> denotes a pause.
I’d been working away this week trying to clear up <,> the backlog of mail caused by me being three weeks away <,> and I thought I was doing marvellously <,> and at about <,> six o’clock last night <,> I was sorting through <,> stuff on the desk and I discovered a fat pile of stuff <,> all carefully opened and documented by Sally that I hadn’t even seen
How many orthographic sentences correspond to the speaker’s story? There is no one correct answer. In writing it we have a choice: we could punctuate it as one sentence or we could split it into two or more sentences, each of the later sentences beginning with and.
Grammarians are not unduly worried about the difficulties in defining the sentence. Their approach to the question is formal because they are interested in grammatical form. Like many people who are not grammarians, they are generally confident of recognizing sentences, and they specify the possible patterns for the sentences. Combinations of words that conform to those patterns are then grammatical sentences.
Irregular sentences and non-sentences
Sentences that conform to the major patterns (cf. 3.13) are regular sentences, and they are the type that will generally concern us in this book. Sentences that do not conform to the major patterns are irregular sentences.
If I ask you to write down the first sentences that come into your mind, you are likely to produce regular sentences. Here are some regular sentences in various major patterns:
David and Helen have three children.
The liquid smelled spicy to Justin.
Some people give their children a daily dose of vitamins.
About a million visitors come to our city every summer.
Most irregular sentences are fragmentary sentences. These leave out words that we can easily supply, usually from the preceding verbal context. Here is a typical example in an exchange between two speakers:
A: Where did you put the letter? B: In he top drawer.
We interpret B’s reply as I put the letter in the top drawer, and that reconstructed sentence would be regular. Similarly, the newspaper headline Washington abuzz over missing intern corresponds to the regular Washington is abuzz over a missing intern. Fragmentary sentences can therefore be viewed as directly derivable in their interpretation from regular sentences.
Finally, we often say or write things that are not grammatical sentences. These non-sentences may simply be mistakes. But they may also be perfectly normal, although they cannot be analyzed grammatically as sentences. Normal non-sentences include such common expression as Hello!; Yes; No; So long!; Thanks!; Cheers!; and they include many headlines, headings, titles, labels and notices:
Traffic Chaos (newspaper headline) On the Nature of the Model (section heading in book) The Captain and the Kings (title of book) Naming of Parts (title of poem) Pure Lemon Juice No Smoking
In the next chapter we will be looking at the patterns of regular sentences, but first I have a few more general things to say about sentences.
Simple and multiple sentences
Here are two sentences placed next to each other:
 The inquiry left in its wake a number of casualties. I was one of them. I can combine the two sentences in  merely by putting and between them:  The inquiry left in its wake a number of casualties, and I was one of them. I can also combine them by putting a connecting word in front of the first sentence:  When the inquiry left in its wake a number of casualties, I was one of them. I can make a small change in the second sentence:
 The inquiry left in its wake a number of casualties, I being one of them.
A sentence or a sentence-like construction contained within a sentence is called a clause. Constructions like I being one of them in  resemble sentences in that they can be analyzed to a large extent in similar ways (cf. 6.8). The sentences in , , and  therefore all consist of two clauses. (Strictly speaking, the separate sentences in  are also clauses, but since they have only one clause each, it is convenient to refer to them just as sentences.)
A sentence that does not contain another clause within it is a simple sentence. If it contains one or more clauses, it is a multiple sentence.
Here are some more examples of multiple sentences with connecting words:
You can’t insist that your children love each other. The building was emptied before the bomb-disposal squad was called. When we returned three hours later, no wolves were in sight. My father always hoped that I would become a doctor and that must have been why he took me along when he visited his patients.
We will be looking more closely at multiple sentences in Chapter 6. Meanwhile, I will be using simple sentences to illustrate general matters about sentences.
There are four major types of sentences:
- Declaratives (or declarative sentences)
She was attracted to an open-air job.
The new proposals have galvanized the normally disparate community into a potent fighting force.
- Interrogatives (or interrogative sentences)
Do you have internet access at home? Where will you be going for your holiday?
- Imperatives (or imperative sentences)
Open the door for me. Take a seat.
- Exclamatives (or exclamative sentences)
How well you look!
What a good friend you are!
These four sentence types differ in their form (cf. 6.2- 4). They correspond in general to four major uses:
Statements are used chiefly to convey information.
Questions are used chiefly to request information.
Directives are used chiefly to request action.
Exclamations are used chiefly to express strong feeling.
It is usual to refer to interrogatives more simply as questions.
We will be discussing these sentence types and their uses in a later chapter (cf. 6.1-5). Declaratives are the basic type and I will therefore generally be using them for illustrative purposes.
Positive and negative sentences
Sentences are either positive or negative. If an auxiliary (‘helping’) verb is present, we can usually change a positive sentence into a negative sentence by inserting not or n’t after the auxiliary. In the following examples, the auxiliaries are
has, is, and can:
Positive: Nancy has been working here for over a year. Negative: Nancy has not been working here for over a year.
Positive: Dan is paying for the meal. Negative: Dan isn’t paying for the meal.
Positive: I can tell the difference. Negative: I can’t tell the difference.
The rules for inserting not and n’t are somewhat complicated. I will return to them
later (cf. 3.3f).
A sentence may be negative because of some other negative word:
She never had a secretary.
Nobody talked to us.
This is no ordinary painting.
Most sentences are positive, and I will therefore generally be using positive sentences for my examples.
Active and passive sentences
Sentences are either active or passive. We can often choose whether to make a sentence active or passive (cf. 4.15). The choice involves differences in position and differences in the form of the verb:
Active: Passive: Charles Dickens wrote many novels.
Many novels were written by Charles Dickens.
Charles Dickens and many novels are at opposite ends of the two sentences. In the passive sentence by comes before Charles Dickens, and the active wrote corresponds to the longer were written. Here are two further examples of pairs of active and passive sentences:
Active: Manchester United beat Liverpool at Old Trafford. Passive: Liverpool were beaten by Manchester United at Old Trafford.
Active: The Rambert Dance Company won the country’s largest arts prize, the Prudential Award. Passive: The country’s largest arts prize, the Prudential Award, was won by the Rambert Dance Company.
Actives are far more numerous than passives. Their relative frequency varies with register. For example, passives tend to be heavily used in formal scientific writing. The nature of grammar as a constituent part of language is better understood in the light of explicitly discriminating the two planes of language, namely, the plane of content and the plane of expression.