A and an are indefinite articles that come before nouns when you aren’t being specific about the thing identified. In other words, you would say

Buy me a coffee mug.

Buy me the coffee mug with the princess on it.

In the first one, we want any old coffee mug, whether it’s a Nascar mug or a boring plain one. But in the second one, we want the specific one, the one with the princess on it. And not just any old gal, the one with the specific princess. Hey, I have three girls and I like princesses. And yes, I’m drinking coffee out of my princess mug right now.

So the difference between the indefinite articles a and an and the definite article the is pretty clear and straightforward. But then there is the usage of a and an, and here, we tend to get tripped up, like a cruel boy and a kid on crutches. Sometimes we fall splat on our face if we don’t consult our local grammar guy or Dr. Google.

The real problem here is with our teachers. Yes, that’s right. Our teachers. In fact, they taught us the wrong rule.  We all learned that we use a before consonants and an before vowels. That’s what I was taught; that’s what my mom was taught back in the day*; that’s what my kids are taught even now. That rule gets you pretty far. About 99% of the time, you will be right. But if you start to use words that begin with h, you’re doomed.

How do you deal with this sentence:

Give me a hour, and I will change your life.

Give me an hour, and I will change your life.

We all hear that the second one is correct, I hope, even though we know it is breaking the rule. H isn’t a vowel, after all, so it shouldn’t use an. Maybe the rule should be changed to something like this:

Use a before consonants and an before vowels, except for h, which should use an.

That helps, but it’s still not right. What about this one:

That boy needs an history lesson.

That boy needs a history lesson.

The second one is correct. Well, shoot, what do we do now?

Use a before consonants and an before vowels, except for h, which can go either way.

Or maybe we just say,

Use a before consonants and an before vowels, except in cases where it doesn’t sound right.

No, I don’t like that. What about

An MC is a person who leads an event.

A monster broke into my backpack and at my homework. (An excuse that may work with the sillier teachers among us. Heck, try it and let me know if it does work.)

In both sentences, there is the indefinite article a or an before a word that starts with m, MC or monster. Why do we use an with MC and a with monster?

Because the sounds at the beginning of the words change. MC actually begins with the eh sound, like enemy. That’s a vowel sound. Just like hour in the example above, which begins with the o sound like our or owl.

So the correct rule, the one we should stick to, the one that will cure the other 1% of our indefinite article ills is,

Use a before consonant sounds and an before vowel sounds.

I will attend a university next year. (the y sound)

She is an unfit teacher. (the uh sound)

I play with a yoyo every day. (the y sound)

I would like to exchange emails with an Homish person. (the o sound)

I would like to have a house without an outhouse (the h sound, the ow sound)

There you have it. Now you know the rule. The problem with not knowing this rule is that it jars us when people don’t do it right. and we don’t want people to pay more attention to how we say something than to the content of what we are actually saying.

*P.S. I hate the phrase “back in the day,” and I advise you to never use it. A future post will explain why, I am sure.