a, an

The decision to use a or an depends on the sound—not the spelling—of the word or abbreviation that follows.

Words

A is used before words that begin with a consonant sound. (In their written form, these words may begin either with a consonant or with a vowel that makes a consonant sound, such as eu, ou, or long u.)

• a book
• a cat
• a house
• a youth
• a European
• a ouananiche (pronounced waw-nuh-nĭsh)
• a use

An is used before words that begin with a vowel sound. (In their written form, these words may begin either with a vowel or with a silent h.)

• an apple
• an egg
• an iron
• an opal
• an umpire
• an ylang-ylang tree (pronounced ĭ-lang-ĭ-lang)
• an hour
• an heir
• an honourable person

Acronyms

The rule stated above for words also applies to acronyms, which are abbreviations pronounced as words:

• a NATO decision (a before the consonant sound n)
• a UNICEF project (a before the long u sound)
• an ACTRA award (an before the vowel sound ă)

Initialisms

In the case of initialisms, which are abbreviations pronounced letter by letter, you must go by the pronunciation of the first letter.

If the first letter begins with a consonant sound when pronounced, then choose the article a:

• a CBC production (starts with the sound s as in see)
• a PhD candidate (starts with the sound p as in pea)
• a UN spokesperson (starts with the sound y as in you)
• a YMCA (starts with the sound w as in why)

But if the first letter in the initialism starts with a vowel sound when pronounced, then choose the article an:

• an FM station (starts with the sound ĕ as in eff)
• an HIV treatment (starts with the sound ā as in aitch)
• an MP (starts with the sound ĕ as in em)
• an RCMP officer (starts with the sound ä as in ar)