1) A: We use “a” before words that begin with consonant sound.

Example: a phone, a car, a motorbike, a train, a school, a building, a hotel, a restaurant…etc.

NOTE: Some words start with a vowel letter but begin with a consonant sound, so we use “a” before these words, too.

Example: a university, a Europe, a one-parent family…etc.

2) AN: We use “an” before words that begin with vowel sound.

Example: an orange, an apple, an egg, an Italy, an umbrella, an axe…etc.

NOTE 1: Some words start with a consonant but begin with a silent sound, so we use “an” before these words as well. These kinds of word always start with letter “h”.

Example: an hour, an honest personnel, an honor, an heir…etc.

NOTE 2: We use “an” before abbreviations said as individual letters that begin with “A, E, F, H, I, L, M, N, OK, R, S, or X”

Example: an MP, an IMF, an FBI agent, an IOU, an HRU…etc.

NOTE 3: We use “a” not “an” before abbreviations said as words.

Example: a NATO general, a FIFA official, a UNECIEF member…etc.

3) ONE

a- We use “one” rather than “a/an” if we want to emphasize that we are talking about only one thing or person rather than two or more.


- Do you have one sandwich or two?

- Are you staying just one night?

- I just took one at her and she started crying.

b- We use “one” in the pattern one…other / another.


- Close one eye, and then the other.

- Bees carry pollen from one plant to another.

c- We use “one” in phrases such as one day, one evening, one spring…etc., to mean a particular, but unspecified day, evening, spring…etc.


- Hope to see again one day.

- One evening, while he was working late at the office.

NOTE 1: We don’t use “one” when we mean ‘any one of a particular type of thing’.


- I really need a cup of coffee.

- You can never find a paper clip in this office.

NOTE 2: We also use “a/an”, not “one” in number and quantity expression such as:

- three times a year, half an hour, a quarter of an hour, a day or so (= about a day)

- 50 pence a liter (notice we can also say ‘…for one liter’)

- a week or two (notice we can also say ‘…one or two weeks’)

- a few, a little, a huge number of…

NOTE 3: We use “a” rather than “one” in the pattern “a…of…” with possessives.


- She’s a colleague of mine.

- That’s a friend of Bill’s.

- It’s a product of Sony Company’s.