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"A" vs. "an"

Sound off

It seems so obvious that we don’t even need to talk about it: We say, “a pencil” but “an eraser,” because the word pencil starts with a consonant and the word eraser starts with a vowel.

That is completely true. The distribution of “a” and “an” is dependent on the sound of the following word, whether it starts with a vowel or a consonant.

It’s completely obvious, but I do want to complicate things a little bit.

Let’s start with just how many vowels there are in the English language. When I was a kid, I learned the vowels in English were a, e, i, o, u, and sometimes y. That gives English about 5.5 vowels.

That rule is really about the way vowels are spelled. When we’re talking about sounds, standard American English has at least 14 vowel sounds, and here they are:

ee, ih, ay, eh, a, oo, eu, oh, aw, ah, uh, ei, ow, and oy.

That’s a lot of vowels. And when those sounds start a word, you typically get “an.”


Unicorn, stock

The loveliest of all…

So let’s talk about unicorns. If a word that starts with a vowel takes “an,” why do we say, “a unicorn?”

I have sometimes asked this question on exams and I’ve gotten some great answers from students, including this one: “Unicorn does not follow the pattern because unicorns are mythical animals.”

Now it’s true that a unicorn is mythical but this is not why the word doesn’t follow the pattern. Unicorn doesn’t follow the pattern because, when you say it, it doesn’t start with a vowel. It starts with a consonant. The sound “yu” is a consonant, so we say, “a unicorn.”

As you can see (or hear!), you have to be careful about spelling versus sound. The word unicorn is an example where a word is spelled with an initial vowel but is pronounced with an initial consonant.

It goes the other direction too, where the spelling has an initial consonant, but the word actually starts with a vowel when it is said out loud. Words that start with “h” are a good example. So in American English the word h-e-r-b is pronounced “erb,” so we say, “an herb.” We also say, “an hour.”

This raises the question of whether, when we’re talking about historical events, it should be “a historical event” or “an historical event.” I would say that if you are someone who doesn’t pronounce the “h” in historical, it should be “an ’istorical event.” For those of us who do pronounce the “h” it should be “a historical event.”

Now you’ll notice that sometimes I say “ay” or “an,” and sometimes I say “uh” or “uhn.”

It primarily depends on whether I am stressing that indefinite article or not. When we are stressing it, we say “ay” and “an.” When we are not stressing it, we say “uh” and “uhn.”

I hope that this has been “ay” useful lesson with “uh” little bit more information about these indefinite articles in English.

This video appears courtesy of LSA Today. Curzan’s observations on language also can be heard on the Michigan Radio program “That’s What They Say.”


  1. William Hettrick - '62, '64, '68 (BMus, MA, PhD)

    This is pretty obvious. In fact, the writer should have delved deeper into history. In the 19th century, at least some American writers (journalists) wrote “an unicorn,” and I suppose that either they may have pronounced the word as “oonicorn” or they were slavishly following the rule in spite of the reason for the rule.


    • Doug Sheridan - MBA 1996

      I disagree. While the issues addressed by the author might have been “obvious” to you, I suspect 5 out of 10 people on the street could not explain the proper use of “a” vs. “an”… and 9 out of 10 could not tell you WHY it is the case (i.e., that it’s based on the sound and not the spelling of the word that it precedes).


  2. Barry Tigay - 1968

    Why is there a pop art picture of a frightened woman in a library being menaced by a shadowy man above the link to this article?


    • Deborah Holdship

      An attempt at a play on horror movies of yore to illustrate the cartoonish “battle” between two words — thus the setting in the library and the exaggerated pop art from a faded movie poster. — Ed.


  3. Valda (Robinson) Byrd - 1976

    Love this article! I was helping my daughter with a paper and trying to explain this very thing. Now I see why if was clear as mud! An hour! It’s how we say it!!! Sometimes


  4. Eric Arnold - '61, '63

    Finally someone whose usage before h-words agrees with my understanding of the use of the indefinite article before h-words! Thank you for that. And thanks for reminding me of the corresponding question regarding unicorns (and unions and universes and universities) but the explanation for that could use some elaboration, I think. The threshold between the sound at the beginning of “unicorn” being a consonant and a diphthong “eu” seems very narrow, and in the case of the word “oink,” I would be likely to say “the pig responded with an oink.” Perhaps you could comment on the difference. Applies to oysters, too…


  5. Richard Helzberg - 62, 65 law

    Definitely an lucid explanation, Anne. I got it!


  6. Matt Muir - 1995

    I guess I see this as a phonological issue. So, for example, as is common across languages, morphemes or words will often change slightly either orthographically and/or in pronunciation in order to differentiate themselves from similar and neighboring morphemes or words that would otherwise interfere with phonologic differentiation by the interlocutor (listener). An example from a Romance language would be Spanish orthographic “y” (“and”) changing to “e” (“and”) when preceding word initial “(h)i…” (e.g., “es fuerte e inteligente” NOT “es fuerte y inteligente”). In the case of the English indefinite article, the change from “a” to “an” protects the indefinite article in spoken language from becoming phonologically undifferentiated and confusing to the listener in cases where the following word has a word initial vowel. “Unicorn”” may be an exception that proves the rule because word initial “un” is sufficiently differentiated from “a” in rapid normal speech and, thus, does not prompt native speakers of English to need an alteration to the article. As for “u” not being a vowel, I’d argue it is indeed a cardinal vowel. “U” also may not prompt the use of preceding “an” because it is a back, closed vowel whereas “a” is a front, open vowel and they are, as such, quite different as vowels go. Sorry, I know that’s pretty technical. Hope it makes sense.


    • Matt Muir - 1995

      I’m feeling internet mortification. I thought it over more after making my first comment (my first mistake). Next, I realized there is an accompanying video as well (mistake number two) which explains things in more depth. The “u” in “unicorn” is definitely not a vowel so what I said about that is all wrong. I fear I made an unfit comment–my mistake.


  7. Will Thomas - 1968

    Basically, use the one that sounds right, which would likely be no help to a non-English speaker.


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