Indefinite article: a and an

The indefinite article in English has two forms: a and an. We use a/an before a singular countable noun when we refer to one person or thing that the listener or reader cannot yet identify, or when we classify it as one member of a group. In contrast, the definite article the is used when the person or thing can be identified.

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A or an?

There are two forms of the definite article – a and an – and we decide which one to use based on the first sound of the following word that it accompanies, not necessarily the noun that it accompanies. A goes before a consonant sound, and an goes before a vowel sound:

Some words that begin with e, o or u are actually pronounced with a consonant sound at the beginning, and are therefore accompanied by a:

• a European country (first sound is/juː/)
• a one-pound coin (first sound is/w/)
• a university (first sound is/juː/)

Some words that begin with h are actually pronounced with a vowel sound at the beginning because the h is silent, and are therefore accompanied by an:

• an honest mistake
• an hour
• an honour

A or an with abbreviations

The same sound rule applies to abbreviations. What matters is how the first letter or syllable is pronounced, not whether it is written with a vowel or consonant letter:

• an FBI agent (first sound is /ef/)
• an MBA (first sound is /em/)
• an SUV (first sound is /es/)
• an X-ray (first sound is /eks/)
• a USB cable (first sound is /juː/)
• a UNESCO report (first sound is /juː/)

A or an with adjectives

If an adjective comes between the article and the noun, choose a or an according to the first sound of the adjective:

• a good idea
• a green apple
• an excellent suggestion
• an orange cat

When to use the indefinite article

The indefinite article a/an is always used with singular countable nouns. The indefinite article tells us that a noun is general, which means the noun is one of a wider group. The following list shows when we use the indefinite article in English.

1. When the listener does not know which one you mean

We commonly use a/an when we refer to one singular countable person or thing that the listener or reader cannot identify. This is often because it is the first time it has been mentioned or because it is one in general out of all the people or things:

• I saw a dog in the park. (the listener doesn’t know which specific dog)
• We stayed in a lovely hotel. (the listener doesn’t know which specific hotel)
• A man phoned earlier. (the listener doesn’t know which specific man)
• I need a pen. (one pen out of all the pens)
• She wants to adopt a cat. (one cat out of all the cats)
• My phone has a camera. (one camera in general)

Once the person or thing has been introduced and is identifiable, we normally use the: I saw a dog in the park. The dog was chasing a ball.

2. To classify a person or thing

We use a/an to say what type or category a person or thing belongs to. This includes jobs and professions.

• She’s a doctor.
• My dad was an engineer.
• Sarah wants to be a dancer when she grows up.
• He’s a genius.
• That was a good idea.
• Daniel is an Englishman.

3. To talk about one example of a whole class of something

We can use a/an + singular countable noun to represent any typical member of a whole class. The plural with no article is often a more natural alternative:

• A dog needs regular exercise. (Dogs need regular exercise.)
• A whale is a mammal. (Whales are mammals.)
• A good dictionary can help you learn vocabulary.

4. With rates, frequency and measurements

We can use a/an to indicate rates, frequencies and measurements as an alternative to per:

• I go to the gym three times a week. (three times per week)
• Take these twice a day. (twice per day)
• This car can go 200 miles an hour. (miles per hour)
• These bananas cost £4 a kilo. (£4 per kilo)

5. In exclamations after what and such

We can use a/an after exclamations what and such to emphasise something:

• What a beautiful day!
• What a fantastic goal!
• You’re such a great friend!
• That was such a terrible film.

6. With numbers and quantities meaning one

Because a/an are used with singular countable nouns, in some situations, we can sometimes use the indefinite article in the same way as one:

• He paid a hundred dollars. (one hundred dollars)
• I need a dozen eggs. (one dozen eggs)
• It will be here in an hour. (one hour)

However, the indefinite article can only substitute for one when counting and referring to an exact number. A/an cannot be used interchangeably with one in other uses of a/an:

• ❌ She is one doctor.
• ❌ What one beautiful day!
• ❌ I saw one dog in the park. (the only time you can say this is if you are literally counting dogs in the park)

When not to use the indefinite article

There are a number of occasions when we cannot or don’t usually use the indefinite article in English.

1. Don’t use a/an with plural nouns

A/an means one, so it cannot be used with plural nouns. With a plural noun that is general or non-specific, we normally use no article or a word such as some to refer to an unspecified quantity:

• ❌ I saw a dogs in the park.
• ✅ I saw some dogs in the park.

• ❌ We bought an apples.
• ✅ We bought some apples.

• ❌ They like a cats.
• ✅ They like cats.

However, if the plural noun is specific or identifiable to the listener, then we would use the definite article the:

• I fed the dogs in the neighbours’ garden.
• The apples in the fridge have gone bad.
• They don’t like the cats that Sophie has.

2. Don’t use a/an with uncountable nouns

Uncountable nouns cannot be counted, not even up to one, and therefore cannot be used with the indefinite article. Like with plural nouns, we usually use no article or a word such as some to refer to an unspecified quantity:

• ❌ She gave me an advice about my job.
• ✅ She gave me some advice about my job. (or a piece of advice)

• ❌ The teacher gave us a homework to do.
• ✅ The teacher gave us some homework to do.  (or a piece of homework)

• ❌ I have a good news.
• ✅ I have good news.

However, some nouns that are usually uncountable can be used with a/an when they have a countable meaning, such as a particular type, instance or serving:

• We had a lovely dinner. (a single instance of dinner)
• Can I have a coffee? (a single serving of coffee)
• You need a good understanding of electronics. (a particular degree of understanding)
• She has a detailed knowledge of the subject. (a particular degree of quality of knowledge)

3. Don’t use a/an when the noun is already identifiable

If the listener or reader can identify which person or thing you mean, use the, not a/an:

• ❌ I bought a book yesterday. A book is excellent. (book is now identifiable)
• ✅ I bought a book yesterday. The book is excellent.

• ❌ Please close a window. (window should be specific)
• ✅ Please close the window.

4. Don’t use a/an before proper nouns or other determiners

We don’t use the indefinite article before proper nouns because their names already identify a specific person, place, organisation, etc. Likewise, we don’t use a/an before possessive or demonstrative determiners because these also identify or specify a noun:

• France (NOT: a France)
• Simon (NOT: a Simon)
• my car (NOT: a my car)
• this idea (NOT: a this idea)

5. Don’t use a/an when a noun stops referring to an individual thing

Some nouns that normally refer to individual people or things are used without a/an in certain situations and expressions. In these cases, the noun refers more generally to an activity, function, method, role or status rather than to one individual person or thing.

Common situations include:

• places and institutions: at school, in prison, at work
• transport and communication: by train, by car, by email
• meals: have breakfast, after lunch, for dinner
• roles and positions: elected president, appointed manager
• states and statuses: on duty, on call, under arrest
• repeated relationships or patterns: face to face, side by side

For example:

• She is at school. (not at a school)
• We travelled by train. (not by a train)
• We had breakfast at eight. (not a breakfast)
• She was elected president. (not a president)

These are examples of bare singular nouns. See the zero article guide for a full explanation and more examples.

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