If the first sound of the following word is a vowel sound (whether or not the letter is a vowel), use an.
an elephant, an hour, an honour, an urn
If the first sound of the following word is a consonant sound (whether or not the letter is a consonant), use a.
a helicopter, a hotel, a union
Using this rule, use an with acronyms such as MRI and STD. (MRI stands for magnetic resonance imaging and STD for sexually transmitted disease.)
an FAQ, an SMS message
Online grammar programs
If you want to learn more about grammar, register for one of Mary’s online grammar courses at www.onlinewritingtraining.com.au
