Confused as to whether you should use a or an? The answer is simple: just pronounce the word that follows the article a or an. The guidelines set forth below will hopefully help you determine the correct usage.
Rules for using a
When the pronunciation is a consonant:
When the pronunciation is a long u:
When the pronunciation is a sounded h
a historic building
Yes, a historic building, not an historic building. Why? Because the h in historic is pronounced. I must admit that in the past I have used an before historic, but I was under the impression that the h was not pronounced. I have since learned that the h is pronounced; thus, I need to say a historic. Not quite sure yet? Pronounce historic. Did the h have a sound or was it silent? A more detailed observation of this issue may be read at http://www.theslot.com/a-an.html.
Rules for using an
When the first sound is a vowel (except a long u, as noted above):
When the first sound is a silent h:
Words beginning with the vowel o may cause some second thoughts. Now remember that the pronunciation of the word that follows a and an will determine which of these two articles to use. As I noted above, you would use an before a vowel sound. So do not be confused when writing, “This is a one-time deal.” Although one-time starts with o, the w sound is what you hear.
The same rule applies to using a or an before an acronym: the initial pronunciation of the acronym rules which article to use.
an MBA (“em-bee-aa”)
an SEC complaint (“ess-ee-cee”)
a DNA code (“dee-en-aa”)
a URL (“you-ar-el”)
I will gladly respond to email inquiries regarding grammar and punctuation issues. If you are having difficulty or just need clarification on a certain subject, please email me and I will do my best to cover the topic in a subsequent article.