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 o
an eggan open windowan 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.

Stuart is an English teacher and runs the Speakspeak website. He currently lives in Prague and has been teaching for over 20 years. Follow Stuart and contact him by subscribing to his monthly newsletter.


  1. Samantha - May 22, 2014, 3:27 pm Reply

    This becomes even more complicated when dealing with words that have two accepted pronunciations- one with a consonant sound and one with a vowel sound. For instance, would you recommend using “a” or “an” before words such as “hour” or “heuristic”?

    • Stuart Cook - May 25, 2014, 10:44 pm Reply

      The ‘h’ in hour is unvoiced, so we definitely say ‘an hour’, not ‘a hour’. The same would go for ‘an honour’, ‘an heir’, and ‘an honest man’.

      It would be ‘a heuristic process’: the ‘h’ in ‘heuristic’ is pronounced /h/.

  2. Eli - June 12, 2014, 9:16 am Reply

    I’m an English teacher and I always find this Web site so informative. Thank you so very much

    • Stuart Cook - June 12, 2014, 10:37 am Reply

      Nice to hear, Eli. Thanks for visiting!

  3. S Rahaman - September 23, 2017, 1:40 pm Reply

    Very nice article and to the point. Brief and accurate. Thank you.

Leave a Reply

Your email address will not be published.

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong>