When to use an and a - articles

Use 'an' if the next word starts with a vowel sound. If it does not, then use 'a'.

Using A and An

There is sometimes confusion about whether to use 'an' or 'a' (particularly with abbreviations). The sound of a word's first letter determines which to use. If the word starts with a vowel sound, you should use 'an'. If it starts with a consonant sound, you should use 'a'.

Examples:

 Buy a house in an hour.  
(Although 'house' and 'hour' start with the same three letters (hou),
one attracts 'a' and the other 'an'.)

 An unknown goblin killed a unicorn.  

 It would be a honour. 
('honour' - starts with an o sound)