a

I = A
a UK [eɪ] / US or A UK / US noun
Word forms "a":
singular a plural a's
Word forms "A":
singular A plural A's

1) [countable/uncountable] the first letter of the English alphabet. A is a vowel.

2) [countable/uncountable] music the sixth note in the musical scale of C major

3) [countable/uncountable] a mark that a teacher gives to a student's work to show that it is excellent

4) [uncountable] medical a common blood group in the abo system

•

- from A to B

See:

A-bomb, A-line, A-list, A-road, A to Z

II = an
a strong UK [eɪ] / US or a weak UK [ə] / US or an strong UK [æn] / US or an weak UK [ən] / US determiner ***

Summary:

A or an is used as an indefinite article, usually followed by a singular countable noun.
A is used when the next word begins with a consonant.
An is used when the next word begins with a vowel sound. When a word begins with the letter "u" that is pronounced /juː/, the word is treated as starting with a consonant: a university. When a word begins with a silent "h", it is treated as starting with a vowel: an hour. The names of the letters f, h, l, m, n, r, s, and x begin with vowel sounds, so abbreviations that begin with one of these letters are treated as starting with a vowel: an MP ♦ an HGV.

1) used when you are mentioning a person or a thing for the first time, or when the person listening to you does not already know about them

I have an idea.

There's a concert on Sunday night.

2) used when you mean any person or thing of a particular type, but you are not referring to a specific one

You need a dictionary.

I haven't got an umbrella.

Children must be accompanied by an adult.

3) used when you say what class, type, or group someone or something belongs to, or what job someone has

He's a liar and a cheat.

Greece has been a republic since 1973.

Ruth's father was a lawyer.

4) used before a singular noun that represents every person or thing of a particular type

A dog needs regular exercise.

A molecule consists of two or more atoms.

5) used when you are referring to a person or thing as one of several people or things of this type

I want you to meet a friend of mine.

He's a member of the team.

6) used in expressions of quantity such as "a lot", "a few", or "a great deal"

a lot of money

a bit of luck

We all appreciate a little encouragement.

7) used in numbers and measurements to mean "one", as in "a thousand" or "an hour"

a million dollars

a hundred years ago

a minute or two

8) used in phrases showing how much something costs, how often it happens, how fast it goes etc

Meetings are held four times a year.

Tomatoes are £1.20 a kilo (= each kilo costs £1.20).

The car was travelling at 90 miles an hour.

9) used before a noun that means a substance, product, food etc when referring to a particular type of it

Brie is a soft creamy cheese.

Plants won't grow in a soil that contains too much lime.

10) used before the name of some drinks to mean a cup or glass of that drink

I'll just have a beer, thanks.

Have you got time for a coffee?

11) used before a noun that means a particular quality or feeling when the quality or feeling is described in some way

Sales staff must have a good working knowledge of French.

They fought back with a fierce determination that surprised the invaders.

12) used before a noun that is formed from a verb and means a single action of that verb

Can I have a try?

Let's take a walk round the garden.

13) used before a noun that expresses your feelings about a situation

It's a relief to know they're safe.

What a shame he couldn't be there to receive the prize!

14) used before the name of a particular day, season, or holiday to mean one particular Tuesday, summer, Christmas etc

It was a bitterly cold winter.

She was born at six o'clock on a Sunday morning.

15) used before a person's name when you do not know anything about them

There's a Mr Alex Murray asking to see you.

a) used before the name of a famous artist to mean a picture by that artist

The gallery has recently acquired a Picasso.

b) used before a family name to mean a member of that family

Remember you're an Osborne – it's a name to be proud of.

c) used before the name of a famous person to mean someone else with similar abilities, a similar appearance, or a similar character

Already he is being hailed as a young Albert Einstein.