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In the following example, is it appropriate to use a or an as the indefinite article, and why?

He ate __ green apple.

I know that in the case of just "apple", it would be "an apple," but I've heard conflicting answers for "green apple," where the noun is separated from the article by an adjective.

Also, which is more appropriate in this case:

He ate __ enormous Pop-Tart.

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This reminds me of the hilarious book English as She Is Spoke, a 19th century guide to English written by a Portuguese man who knew no English. Among the other ridiculous errors, the author appeared to believe that English nouns were either masculine or feminine and that "a" was used for masculine, "an" for feminine nouns. –  Joel Spolsky Aug 6 '10 at 17:16

11 Answers 11

up vote 105 down vote accepted

The question of "a" vs "an" is always decided by the pronunciation of the word that follows the article. Thus, various geographical regions that have different pronunciation rules may use a different article for the same word.

Words that begin with a vowel sound, such as "apple", "egg", or "hour" are preceded by "an".

All other words, such as "cake", "pie", and "user" (which begins with a y sound), are preceded by "a".

Except (as lifted from @Nohat's comment below) - The rules before "h" are a little tricky, but clear: if a word begins with an "h" sound and the first syllable is stressed (like "hotel"), then it never takes "an". If the first syllable is not stressed (like "historical") then it is possible to use "an". Some usage authorities would say you must use "an" in those cases, but Nohat is not one of those authorities. You find both "a" and "an" used before words like "historical".

So to answer your actual question:

He ate a green apple.
He ate an enormous Pop-Tart.

"Green" does not begin with a vowel sound, so we use "a".
"Enormous", on the other hand, does begin with a vowel sound, so we use "an".

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@Kinopiko: At least in many dialects I've heard, "user", "European", etc. begin with the same (similar?) sound that many words starting with "y" do, thus a "y sound" (probably represented by a 'j' in more formal representations). –  ShreevatsaR Aug 6 '10 at 3:35
@Kinopiko, it most certainly does! What sound do you think it starts with? –  nohat Aug 6 '10 at 4:46
@Kinopiko, I think what people mean by a "y sound" is the palatal approximant (en.wikipedia.org/wiki/Palatal_approximant) because that is the sound that the letter 'y' corresponds to in prototypical cases, such as in the word "yes". Are you saying that the palatal approximant is not a sound, or that "y sound" is not a valid way to refer to the palatal approximant? –  nohat Aug 6 '10 at 6:26
The rules before "h" are a little tricky, but clear: if a word begins with an "h" sound and the first syllable is stressed (like "hotel"), then it never takes "an". If the first syllable is not stressed (like "historical") then it is possible to use "an". Some usage authorities would say you must use "an" in those cases, but I am not one of those authorities. You find both "a" and "an" used before words like "historical". –  nohat Aug 6 '10 at 18:39
In what dialect is "hotel" stressed on the first syllable? –  user16269 Feb 27 '12 at 7:39

There is a bizarre urban legend of sorts that you're "supposed to" use "an" if the head noun in the noun phrase it determines begins with a vowel sound, rather than the first word in the noun phrase, giving rise to claims that "an green apple" is somehow "technically" correct. Here is a blog post of someone who seems to have gotten this idea. And here is the discussion on Language Log about that blog post.

In any case, the rule is that you use "an" if the next word begins with a vowel sound. Vowel sound is crucial here because many words that begin with vowel letters do not begin with vowel sounds (e.g. user) and vice versa (e.g. hour).

This makes it a kind of sandhi rule for "intrusive N" in English for indefinite articles, avoiding hiatus between the article and the following word.

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But what's the reasoning behind this alternation? Is it syntactically motivated? Phonologically? –  Charlie Aug 6 '10 at 4:59
I thought you were going to say there is an urban legend that if you misuse an "an" you would shot by an arrow or something. Rather disappointed now. –  burnt_hand Aug 6 '10 at 16:28
@itrekkie, it seems you answered your own question far better than I could have ;-) –  nohat Aug 6 '10 at 16:43
+1 for clearing up any confusion. That blog post is hilarious; full-on outrage against an imaginary feature of English grammar. :-P –  Jonik Aug 19 '10 at 2:45
@Pacerier The first sound of the word "user" is a palatal approximant, which is a consonant, not a vowel. –  nohat May 10 '12 at 22:19

As said, an before vowels and a otherwise. We know how/when, but not why.

According to Asudeh and Klein, the morpheme for the English indefinite determiner is represented by three different allomorphs ([ə], [ən], and [ej]—though I disagree with schwa slightly, it's the same in spirit), whose appearance is phonologically determined. When the morpheme is immediately followed by a segment marked by [+continuant], [ən] is selected, and if [-continuant], [ə]—the final form is uttered in isolation. —I question their use of [+continuant] instead of the traditional "vowel": this doesn't handle the the case of fricatives: *"an sister"; or approximates: [+continuant, +sonorant], *"an yacht".

What's really interesting here is that they mention a work by Harris that says that this is a form of deletion, that [ən] is the underlying form and deleted where the [n] cannot fill the onset of the following syllable. This begins to explain why an won't work before vowels.

Finally, it's interesting to know that this was a source of great debate for many years. A lot of people argued that this was anything but phonologically determined, wasting a ton of time and effort. Pay attention to phonology!

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I loled at the last link. –  nohat Aug 6 '10 at 6:31
+1 for the link. I laughed out loud. –  Kalamane Jul 27 '11 at 20:55
Thanks to you, I have now overgrown my browser's capacity for bookmarks. My family will be complaining even more now that I have further escapes to seize! LOL –  TheGeeko61 Jan 14 '12 at 2:45
Re "This begins to explain why an won't work before vowels", is vowels actually the word you wanted? –  jwpat7 May 8 '12 at 6:33
You have a huge typo here that you need to edit!!! "an won't work before vowels. You mean consonants right? –  Araucaria Jun 6 at 20:30

Have you really heard conflicting answers? I'm not aware of any controversy amongst native speakers on this issue.

a green apple

is correct.

This is decided by pronunciation, nothing more.

Similarly for the two pronuncations of "the" (ði: and ðǝ).

"He ate [insert here] enormous Pop-Tart."

"an" is correct here, it's decided by pronuncation of the following word, nothing more.

The only instance of a/an controversy amongst native speakers which I'm aware of is "a/an historical", with "an historical" plus aspirated "h" being preferred by some speakers.

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Personally, I'm quite happy with waiwai's answer and many of the other points made here. However, one point not really addressed so far is why this rule is so.

The answer is fairly simple. For native english speakers, it's easier to physically say 'an apple' rather than 'a apple', 'an hour' rather than 'a hour'.

I'm sure speech therapists can explain technically in terms of phonation and resonance, but it's not my area of expertise.

It's understandable therefore, that some non-native English speakers might be puzzled - since their vocal chords may be trained differently.

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"an" before vowels, and "a" before everything else.

Except for a few exceptions...

Words that begin with a consonant, but sound like they begin with a vowel, I've always understood them to be proceeded by "an" since they begin with a soft sound (eg - An heirloom).

As already pointed out by another answer, "user" starts with a vowel, yet is preceded by "a" because it begins with a hard sound.

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"begin with a verb" -> "begin with a vowel", I believe you mean. –  Jared Updike Aug 6 '10 at 4:46
@Jared - thanks!! –  Jagd Aug 8 '10 at 3:25

Language is most easily spoken and listened to when there is an alternating pattern between consonants and vowels. It's very easy for the ear to distinguish between vowels and consonants, but not so easy when they are clumped together.

An easily spoken sentence would look like this:

vowel consonant vowel consonant vowel consonant vowel consonant vowel consonant

To maintain this pattern while using an indefinite article, it's necessary to insert a consonant (n) between two vowel sounds or remove the n between a vowel and consonant, whichever way you prefer to view it.

An apple is easier to speak and hear than a apple. A bear is easier to speak and hear than an bear. An IBM employee is easier to speak and hear than a IBM employee.

Some regional dialects actually do not pronounce their "h", such as British English. In those regions, it's easier to speak and hear "an historic event" than "a historic event".

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I think what is going on with historic is subtler than that. Many Americans pronounce the "h" in historic, (and other words beginning with h in a non-accented syllable), if and only if the word before ends with a vowel (or if it comes after a natural pause in speech). So with this rule, "a historic" and "an istoric" are both valid pronunciations. Which one is right? I believe a sizeable minority of Americans say "an istoric". –  Peter Shor Jul 28 '11 at 16:55

The rule for using the article a versus an is exactly the same as the rule governing whether one pronounces the article the as /ðə/ or as /ði/.

Both rules operate for the same reason: they make it easier to pronounce and understand an article as distinct from the NP following it. If that NP starts with a vowel sound, we change the article’s pronunciation.

  • an abusive case [RIGHT]
  • *a abusive case [WRONG]

If you did it the wrong way, the article would collide with what came afterwards.

It is the same with the, but here it is reflected in pronunciation alone.

  • the /ði/ aforementioned case [RIGHT]
  • the */ðə/ aforementioned case [WRONG]

If you do either article the wrong way, they will get lost in speech, which will make things harder to understand.

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The five-dollar word for this is sandhi. –  RegDwigнt Dec 19 '13 at 18:20

In addition to the answers here, consider this non-trivial example - (from Life, the Universe and Everything by Douglas Adams):

"I think, that there's an SEP over there"

Now here "a SEP" would do as well, but then you would have to pronounce it "sep" instead of "es-ee-pee" which is what the author meant. E, in "es" is a vowel.

Another less trivial example is "an hour". 'h' is a valid and pronounced consonant, but it still doesn't count.

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Do you pronounce the 'h' in hour? I certainly don't. –  Mr. Shiny and New 安宇 Aug 16 '10 at 13:12
The "h" in hour is not pronounced in American English. –  ssakl Feb 28 '11 at 22:42
@ssakl. It's not pronounced in any English dialect I know of. –  TRiG Jan 1 '12 at 23:49

It depends on the sound of the word following the article. If the following word has a vowel sound, use an. If the word has a consonant sound, use an a.

See.Purdue Notes

There are a few exceptions to this.

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If this weren't a duplicate, surely it would be general reference? –  Edwin Ashworth Sep 3 at 16:46
@Edwin Ashworth Agreed that this would be general reference. However, many of us prefer the StackExchange question answer format as a reference. –  id.ot Sep 3 at 16:59
@id.ot Many of us would prefer to have all the money richer people have. –  Edwin Ashworth Sep 3 at 17:14
@EdwinAshworth Figure that one out and I'll 'star' it. –  id.ot Sep 3 at 17:43

If a vowel SOUND (a, e, o, i) follows, bar y & u, "an" MUST be used, as shown in the examples below:--

An array of delicacies. An enormous man. An Iraqi citizen. An obscure location.

But don't be fooled: if the word following "an" begins with a CONSONANT sound, u & y included here, "a" must be used, instead. Like this:--

A utopia of the present. A yearning. A black man of benevolence. A zebra from Africa.

So in summary, if a word that is immediately after a/an has a vowel sound, "an" must be used; if a word that is immediately after a/an has a consonant sound (which includes the sound y, which is taken on by the letters u & y), "a" is to be used.

Tip: regard the sounds rather than the letters when determining which to use. Soon, it'll come naturally.

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protected by RegDwigнt May 19 '11 at 8:22

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