More about a/an

Countable and uncountable nouns

Countable nouns are the names of separate objects, people, ideas, etc which we can count.

• a cat – three cats
• a secretary – four secretaries
• a plan – two plans

Uncountable nouns are the names of materials, liquids and other things which we do not usually see as separate objects.

• wool (but not a wool, two wools)
• water (but not a water, three waters)
• weather (but not a weather, four weathers)
• energy (but not an energy, several energies)

note

For more detailed information, (see here).

a/an with singular countable nouns

We normally use a/an only with singular countable nouns.

• a secretary
• an office
• but not a salt or an offices

note

For expressions like a good two hours, (see here).

Uses of a/an

A/an does not add much to the meaning of a noun – it is like a weak form of ‘one’. It has several common uses.

One person or thing

We can use a/an when we mention one person or thing for the first time.

• There’s a police car outside.
• My brother’s married to a doctor.
• Andy lives in an old house.

Any one member of a class

We can use a/an when we talk about any one member of a class.

• A doctor must like people. (= any doctor)
• I would like to live in an old house. (= any old house)

Classifying and defining

We can use a/an when we classify or define people and things – when we say what they are, what job they do, or what they are used for.

• She’s a doctor.
• I’m looking forward to being a grandmother.
• A glider is a plane with no engine.
• Don’t use your plate as an ashtray.

Descriptions

A/an is common before nouns that are used in descriptions.

• She’s a nice person.
• He’s got a friendly face.
• That was a lovely evening.
• It’s an extremely hot day.

When a/an cannot be left out

We do not normally leave out a/an in negative expressions, after prepositions or after fractions.

• ‘Lend me your pen.’ ‘I haven’t got a pen.’ (not I haven’t got pen.)
• You shouldn’t go out without a coat. (not … without coat.)
• three-quarters of a pound (not three-quarters of pound)

And we do not leave out a/an when we say what jobs people have, or how things are used (see above).

• She’s an engineer. (not She’s engineer.)
• I used my shoe as a hammer. (not … as hammer.)

When a/an is not used: adjectives alone; possessives

A/an cannot normally be used with an adjective alone (without a noun). Compare:

• It’s a good car.
• It’s good. (not It’s a good.)

A/an cannot be used together with a possessive. Instead, we can use the structure a … of mine/yours, etc (see here).

• He’s a friend of mine. (not He’s a my friend.)

a/an and the

Instead of a/an, we use the when we want to say ‘You and I both know which one I mean’. Compare:

• She lives in a big house. (The hearer doesn’t know which one.)
• She lives in the big house over there. (The hearer knows which one.)

For details, (see here).

a and an: the difference

We do not normally pronounce the sound /ə/ before a vowel. So before a vowel, the article a (/ə/) changes to an (/ən/). Compare:

• a rabbit
• a lemon
• an elephant
• an orange

The choice between a and an depends on pronunciation, not spelling. We use an before a vowel sound, even if it is written as a consonant.

• an hour /ən ˈaʊə(r)/
• an MP /ən em ˈpiː/

And we use a before a consonant sound, even if it is written as a vowel.

• a university /ə juːnɪˈvɜːsəti/
• a one-pound coin /ə ˌwʌn ˌpaʊnd ˈkɔɪn/

Some people say an, not a, before words beginning with h if the first syllable is unstressed.

• an hotel (a hotel is more common)
• an historic occasion (a historic … is more common)
• an hypothesis (a hypothesis is more common)
• but not an housewife – the first syllable is stressed.

A is sometimes pronounced /eɪ/ before a hesitation, when we want to emphasise the following word, or when we want to make a contrast with the.

• I think I’ll have a /eɪ/ – chocolate ice cream.
• It’s a /eɪ/ reason – it’s not the only reason.