A or an

Abbreviations and acronyms

Use 'an' if an abbreviation or acronym starts with a vowel sound. Use 'a' if it doesn’t. For acronymns, this applies whether you say it as a word or the individual letters (initialism). For example:

• a NASA astronaut
• an Interpol employee
• an RPS permit (arr, pee, ess)
• a DNA test (dee, en, aay)

Words starting with 'h'

In most cases use 'a' before a word beginning with 'h'. But use your judgement, if you think that sounds odd, try 'an' instead. Technically, if:

• you fully pronounce the 'h', as in 'hotel' or 'hair', you should use 'a'
• the first sound in the word is a vowel, as in 'hour' or 'heir', you should use 'an'