The head of a noun phrase
The head of a noun phrase either takes the form of a noun or a pronoun. The head determines such features of the noun phrase as number (singular or plural) and gender (masculine, feminine or neuter). In terms of meaning, the head determines what kind or type of entity the whole noun phrase refers to.
Thus, the following noun phrases have the same noun, car, as head and therefore refer to the same kind of entity, namely some kind of car. The exact reference of the full noun phrases differ because of the different determiners and modifiers that accompany the head.
(1) the blue car that Lisa bought
(2) the yellow car that is parked outside my office
(3) a French car with four-wheel steering
Nouns can be grouped into different classes based on their grammatical properties.
Proper nouns and common nouns
A first major distinction among nouns is that between proper nouns and common nouns. Simply put, proper nouns are nouns that functions as names of people, cities, countries, etc. Typical examples are: Bill, Stockholm, and Denmark. All other nouns are common nouns, e.g. car, water, and democracy.
The distinction is relevant to capitalisation. Thus, proper nouns always start with a capital letter.
Since proper nouns are used to refer to unique individuals, places, and so on, they do not show a distinction between definite and indefinite forms, which for common nouns is signalled by the definite and indefinite articles. Most proper nouns occur without an article, like Sweden, Lund, Bill, etc. However, there are also classes of poper nouns which have a definite article as part of their name. Examples include names of daily newspapers (The Times, the Observer, etc.), names of theatres, museums, hotels, restaurants, and similar establishments (the Metropolitan, the British Museum, the Hilton, the Ritz, etc. If the name of such an establishment consists of a noun or noun phase in the genitive, then even these proper nouns occur without an article (McDonald's, Sloppy Joe's).
Proper nouns in the plural form another important class that occur with the definite article. Typical examples include names of mountain ranges (the Himalayas), groups of islands (The Canaries), and others (the Midlands, the Neherlands, the Balkans).
Countable and uncountable nouns
Common nouns may be divided into countable and uncountable nouns. As the terminology suggests, countable nouns can combine with numerals like one, two, three, etc., whereas uncountable nouns cannot. Moreover, uncountable nouns are always singular, whereas most countable nouns may be either singular or plural. A number of properties related to this basic difference distinguish the two classes of nouns. The following table lists the most important ones, and provides examples of both types of noun. (The asterisk * marks an example as ungrammatical.)
accept the indefinite article:
do not accept the indefinite article:
typically have a plural form:
have no plural form:
can, and sometimes must, be replaced by the pronoun one:
cannot be replaced by the pronoun one:
in the plural, combine with plural quantifiers like many, a great number of, etc.:
only combine with singular quantifiers like much, a great deal of, etc.:
Inherently plural nouns
Some nouns are such that they cannot be used in the singular, that is, they are always regarded as denoting something plural, and they always take plural agreement. Important members of this category appear in the following examples:
(4) My new jeans are Italian.
(5) We have to buy Peter new pyjamas, since his old ones are worn out.
(6) In this experiment, headphones are to be used.
(7) The ship's doctor made use of tweezers to remove the foreign object.
(8) The minutes were kept by Sheila.
(9) The goods have been exported to Germany.
(10) All our valuables have been stolen.
(11) The police are investigating the case.
(12) There were hundreds of police present in Stockholm in connection with the royal wedding.
(13) Do you know how many people are here?
(14) The cattle were seen grazing in the field.
(15) We do not want vermin in our house, but they are here anyway.
Nouns in -ics
Nouns that end in -ics look plural, but are actually most often treated as singular. Thus, when heading a noun phrase which functions as the subject, they trigger singular agreement on the verb.
(16) Statistics is becoming increasingly popular among our students.
(17) Mathematics is an integral part of our culture.
(18) Western economics has tended not to be influenced by theories from other parts of the world.
In the examples above, the nouns in -ics denote academic disciplines. However, some of these nouns may also be used to denote the practical application of the discipline, and are then treated as ordinary plurals, e.g. by taking plural determiners and by triggering plural agreement on the verb.
(19) These statistics show that our production of beef has almost doubled.
(20) The acoustics of the new concert hall are very lively.
Zero plural nouns are nouns that look the same in the plural as they do in the singular. A well-known example is the noun sheep. Since sheep is a zero plural noun, it looks the same in the two sentences below. However, this does not prevent it from being singular in the first sentence and plural in the second one, as indicated by the different verb forms, is and are:
(21) My sheep is black.
(22) My sheep are black.
Other nouns that belong to this category are aircraft, Chinese, deer, elk, headquarters, horsepower, hovercraft, means, offspring, Portuguese, salmon, series, species, trout, and Vietnamese. When in doubt, please consult a good dictionary.
There is a group of nouns whose members are commonly referred to as 'foreign plurals'. What the nouns in this group have in common is that both their singular and their plural forms have been borrowed from other languages, which means that the plural ending is not the regular English -s, but something else.
Examples of such foreign plural nouns that are important to remember, especially when writing academic texts (since many of these words tend to be academic in nature), are analysis-analyses, basis-bases, criterion-criteria, diagnosis-diagnoses, hypothesis-hypotheses, parenthesis-parentheses, phenomenon-phenomena, stimulus-stimuli, and thesis-theses.
What usually happens when a word is borrowed into English (or into some other language) is that it is changed in line with the morphology of the language into which it has been borrowed. Consequently, there are some foreign words in English that have both a foreign and an English plural form. Examples include appendix-appendixes/appendices, cactus-cactuses/cacti, focus-focuses/foci, and index-indexes/indices.
A couple of etymologically plural nouns are sometimes used as (uncountable) singulars. The two most common examples are media and data. The singular uses are not universally accepted, however, so non-native writers are well-advised to use them as plurals in examples like the following:
(23) These data show that our initial assumption was right.
(24) The media have become more interested in environmental issues.