When to use “a” or “an”
Ask about the spelling rule for using ‘a’ or ‘an’ before a word and you’ll probably hear:
- ‘a‘ before words beginning with a consonant
(‘b’, ‘c’, ‘d’, ‘f’, etc.);
- ‘an‘ before words beginning with a vowel
(‘a’, ‘e’, ‘i’, ‘o’, ‘u’).
So we say: a banana, a pear, a blue sky, a huge house
an orange, an egg, an open window, an interesting film.
But there is a problem here. Based on this rule, we would have to say ‘a hour’ and ‘an one-week holiday. Both, however, would be wrong. It should be ‘an hour’ and ‘a one-week holiday’.
So, it is not enough to look at the first letter of the word. The thing which we have to consider is the pronunciation of that first letter.
A more accurate rule is therefore:
- use ‘a‘ before a consonant sound;
- use ‘an‘ before a vowel sound.
Here are some examples to illustrate this, using letters which can have both a vowel and consonant sound:
- a house (the ‘h’ in ‘house’ is pronounced /h/)
- BUT an hour because the ‘h’ in ‘hour’ is not pronounced
- a happy man (the ‘h’ in ‘happy’ is pronounced /h/)
- BUT an honest man because the ‘h’ in ‘honest’ is not pronounced
- an umbrella (the ‘u’ in ‘umbrella’ is pronounced as a vowel)
- BUT a university because the ‘u’ in ‘university’ is pronounced like a ‘y’
- an office (the ‘o’ in ‘office’ is pronounced /o/)
- BUT a one-way street because the ‘o’ in ‘one’ is pronounced /w/.
Be careful with abbreviations:
- a Member of Parliament
- BUT an MP because the ‘m’ here is pronounced /em/.
Some other examples of abbreviations being preceded by ‘an’:
- an MBA
- an NGO
- an RAF pilot
- an SOS signal.
This is all we have to remember: the use of ‘a’ or ‘an’ is determined by the sound that follows. We don’t need to think about whether the first letter of the next word is a consonant or vowel.
The rule applies to both written and spoken English.