Grammar Girl here.
Today's topic is a versus an.
A lot of people learned the rule that you put a before words that start with consonants and an before words that start with vowels, but it's actually a bit more complicated than that. For example, here's Matthew with a question:
I've been wondering if it is actually a hour or an hour. An hour sounds more correct, but a hour reads more correct. I'm just curious on what it should be.
The rule is that you use a before words that start with a consonant sound and an before words that start with a vowel sound (1).
So to answer Matt's question, an hour is correct, because hour starts with a vowel sound. People seem to ask most often about words that start with the letters h and u because sometimes these words start with vowel sounds and sometimes they start with consonant sounds. For example, it is a historic monument* because historic starts with an h sound, but it is an honorable fellow because honorable starts with an o sound. Similarly, it is a Utopian idea, but an unfair world.
The letters o and m can be tricky too. Usually you put an before words that start with o, but sometimes you use a. For example, you would use a if you were to say, “She has a one-track mind,” because one-track starts with a w sound. Similarly, “She has an MBA, but chooses to work as a missionary.”
Other letters can also be pronounced either way. Just remember it is the sound that governs whether you use a or an, not the actual first letter of the word.
One complication is when words are pronounced differently in British and American English. For example, the word for a certain kind of plant is pronounced “erb” in American English and “herb” in British English. In the rare cases where this is a problem, use the form that will be expected in your country or by the majority of your readers.
Web Extra
A and an are called indefinite articles. The is called a definite article. The difference is that a and an don't say anything special about the word that follows. For example, think about the sentence, “I need a horse.” You'll take any horse—just a horse will do. But if you say, “I need the horse,” then you want a specific horse. That's why the is called a definite article—you want something definite. At least that's how I remember the names.
I find it interesting that there are two words for the indefinite article (a and an) depending on the word that comes next, but there is only one definite article (the). But, there's a special pronunciation rule about the word the that is similar to the rule about when to use a and an: The is pronounced “thuh” when it comes before a word that starts with a consonant sound, and it's pronounced “thee” when it comes before a word that starts with a vowel sound. It can also be pronounced “thee” for emphasis (2), for example if you wanted to say, “Twitter is the [pronounced “thee”] hot social networking tool.” I actually have trouble remembering this rule and have to make special marks in my transcripts to remind myself to get the pronunciation right, so I apologize if I mess it up sometimes. I think I must have missed the day they covered this in school, and I've never recovered.
That's all.
