Two nouns referring to the same idea are often placed next to each other, sometimes with bracket-like commas around the second
DEFINITION AND GENERAL PURPOSE OF APPOSITION
Two nouns (or noun phrases) placed directly next to each other can do very different things. The first might resemble an adjective describing the second (see 38. Nouns Used Like Adjectives), or make a list with it (see 50. Right and Wrong Comma Places), or name an owner of what it represents (see 58. Optional Apostrophe Endings). In the kind of noun pair that I want to examine here, both of the nouns have similar meaning, like this:
(a) Two main ethnic groups populate Sri Lanka, an island south of India.
Here there are two noun phrases referring to the same island. They are different from the similar-meaning nouns discussed in the post 5. Repetition with Synonyms in that they are not separated by other words, and they differ from the kind of pairs considered in the post 92. Complement-Showing “As” in that the verb (populate) has nothing to do with their being together (it does not behave like CALL or MAKE).
The kind of noun pairing shown in (a) – sometimes with separating commas, sometimes not – has the technical name of “apposition”. Its purpose is to give the reader or listener a better idea of what the nouns mean. It usually involves just two nouns or noun phrases, but more than two are possible. It can be classified into different types according to the kinds of noun phrases involved. This post is about these various types of apposition, as well as their punctuation.
One form of apposition that I am not considering here, though, is where the second noun stands for part of the idea of the first, whether as a random example (after for example, such as or like) or as the part most deserving of a mention (with particularly, notably or especially). More about example-giving apposition is in the posts 1. Simple Example-Giving, 53. “As”, “Like” and “Such As”, 54. Sentence Lists 1: Incidental and 96. Hedging 2: Lists & Predictions.
THE MAIN TYPES OF APPOSITION
Apposition structures can be classified according to the kind of information that they give. They may be describing something named by the first noun, or naming something first described by it, or presenting an alternative name for it. These are all types of “good” repetition (see 24. Good and Bad Repetition) that can also be achieved by placing whole sentences together (see 18. Relations Between Sentences).
1. The Describing Use
The following sentences have this use:
(a) Two main ethnic groups populate Sri Lanka, an island south of India.
(b) Mount Kilimanjaro, an extinct volcano, is the highest in Africa.
(c) The defendant, a man of 45, was led in by two policemen.
(d) Ringo Starr, the Beatle drummer, was the last to join the group.
(e) Apposition, the juxtaposition of two or more nouns referring to the same thing, is a notable feature of professional writing.
(f) Felis leo, (in other words) the lion, is the acknowledged “king” of the cat family.
In all of these, the first noun mentions a name or other idea and the second describes it (for more on names versus descriptions, see 62. Choices with Capital Letters). The link between the description and the name seems to be a new one for the addressee (i.e. not already known – see 156. Mentioning what the Reader Knows Already).
Two kinds of “description” are shown above. The first, in sentences (a) – (d), is the more familiar kind: the second noun phrase links the first with a characteristic that other noun ideas could also possess. For example, the second noun phrase an extinct volcano could characterise many mountains besides Kilimanjaro.
The second kind of “description”, shown by the second noun expressions in (e) and (f), is actually defining, since it is not applicable to other nouns. Apposition-style definitions are likely to accompany expressions that the writer expects the reader not to understand. Readers who encounter such expressions need to be able to recognise apposition-style definitions in order not to waste time guessing their meanings or consulting a dictionary (see 177. How to Guess Meanings in a Text). Help is sometimes available from the presence of in other words or that is to say before the second noun expression.
In all of the above sentences, the second noun expressions are between two bracket-like commas (or a comma and a full stop). This use of commas is considered in detail in the post 50. Right & Wrong Comma Places. There is perhaps just one situation where it does not accompany descriptive apposition. Consider this:
(g) Paris the capital of France has a long history.
Unlike most of the first nouns above, Paris is a name with more than one owner – the other being a town in Texas, USA. Because of this, there will sometimes be a need to clarify which Paris is being talked about. This is what absent commas do in sentences like (g). The same thing happens in John the Baptist, Jack the Ripper and Ford the motor manufacturer. The presence of commas in (g) would suggest that the reader was unlikely to be confused about which Paris was meant, but needed to be reminded or informed of its French-capital characteristic.
This choice concerning commas in sentences like (g) is identical to the one in sentences containing who, which or that (see 34. Relative Pronouns and Commas). This is not surprising, since a paraphrase with a relative pronoun is usually possible: the Paris that is the capital of France in (g). More can be read about such sentences in the post 47. Article Errors with Proper Nouns.
2. The Naming Use
Here, the two types of noun phrase are the same as above, but in reverse order with the more descriptive one first:
(h) The upmarket cars Mercedes and Rolls Royce have iconic radiator designs.
(i) (The) Beatle John Lennon was killed in 1980.
(j) The article “a” is not possible with many nouns.
(k) An article, (namely) “the”, is usually needed with superlative adjectives.
(l) The Beatle drummer(,) (namely) Ringo Starr(,) was the last to join the group.
(m) The definite article(,) (namely) the(,) is not common before a generalising plural noun.
A major reason for sequencing the noun phrases this way round seems to be a recognition that the reader already associates the initial descriptive fact with the subsequent name. This seems to be the situation in all of the above except (l) and (m) written with commas.
Sometimes the second noun phrase is a list of names. This is the case in (h) above (Mercedes and Rolls Royce). More about this use of lists is in the post 54. Sentence Lists 1: Incidental. Naming without listing is also considered in greater detail elsewhere within these pages – see 117. Saying More Precisely What is Meant. Apposition is only one of three main ways of achieving it.
It will be seen that the apposition lacks commas in (h), (i) and (j) above, needs them in (k), and allows a choice in (l) and (m). Wherever commas are used, namely can be added before the second noun phrase. The reason for their need in (k) seems to be the absence of the before the first of the two nouns (cf. an article).
The comma choice in (l) and (m) is probably because the two parts of the apposition there are exactly equal: Beatle drummer always means only Ringo Starr, and definite article refers only to the. In all of the other sentences, the first noun phrase by itself (without the) could refer to other possibilities than those mentioned. Upmarket cars in (h) could represent Chevrolet or Ferrari; Beatle in (i) could indicate Ringo Starr or Paul McCartney; and article in (k) could mean a as well as the.
Sentences like (l) and (m) written without commas seem very similar to (i). However, with commas the suggestion is that the connection between the initial description and the subsequent name is not familiar to the addressee – for example that they do not know who the Beatle drummer is. The second noun phrase, surrounded by commas, supplies this missing information.
Sentence (i) is the only one where the is shown as optional before the first part of the apposition (Beatle). Dropping it is a specialised use often found in newspapers (see 166. Appropriacy in Professional English). It is possible when two conditions are met. The first noun must be a human description (which Beatle is), and it must not be followed by a comma. These conditions are also met by (l) when it is written without commas.
3. The Name-Presenting Use
Sometimes the second noun phrase in an apposition construction does not describe or name the first one in any way, but is instead merely a different name that is not expected to be familiar to the reader. Here is an example:
(n) The shoulder blades, (in other words) the scapulae, are in a posterior position just below each shoulder.
A major reason why technical names like scapulae exist alongside everyday ones like shoulder blades is that scientific study has found a problem with the everyday name that is avoided by creating the technical one and defining it in a particular way. A probable reason for giving both names in sentences like (n) is in order to teach the technical name to the reader, who is perhaps expected to be a student. Starting with a familiar name before linking it with a new one is a classic way to assist understanding and memorization.
The punctuation of this apposition type is always two commas. Other possible linking expressions between the nouns are that is to say and or (without a following the).