My friend is implementing an app for Amazon Alexa which currently speaks the indefinite article "an" in noun phrase acronyms which start with the letter 'U', for example:

(1.) *I found out he was an U.S. president.

My idiolect prefers "a" here instead, presumably because my aggregated experience of the "a/an" contrast perceived this as a rare (unique?) case where English formally licenses a syntactic alternation (insofar as spelling is overt syntax, and syntax is formal) driven by phonotactic considerations.

So much for the grade-school rule-of-thumb about "whether the spelling starts with a vowel." In any case, I'm a native speaker and it does seem to be the case for me:

(2a.) I'm an unhappy camper.
(2b.) Bob is a used car salesman.

Since "U.S." in sentence (1) is pronounced in as in (2b), I prefer the phonologically reduced form:

(3) I found out he was a U.S. president.

Apparently contradicting this idea is the evidence of native speakers who insist on "an" for words starting with 'H'.

(4) ?It was an historic victory.

I marked (4) questionable to indicate that it's not in my idiolect. My question is, without devolving into a prescriptive/descriptive debate, are there other considerations beyond what I've mentioned here that could explain or underlie the observed alternation?

  • 2
    Every (modern) English speaker uses "a" in "a U.S. president" as far as I know. There are many similar cases such as "a universe", "a use," "a utopia", "a eulogy".
    – herisson
    Jan 31, 2017 at 6:43
  • I think my answer to the following question gives a fairly complete description of a/an usage; if I left something out hopefully someone can let me know: When should I use “a” vs “an”? As you note, it's based on the phonology of the word, not the spelling.
    – herisson
    Jan 31, 2017 at 6:44
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    (4) Is pretty much exclusively a Boston, or at least New England accent. Unless Alexa is a Bostonian you shouldn't follow that rule. And, given that she's an Amazonian she really ought to speak with a Seattle accent and not a Bostonian one.
    – ohwilleke
    Jan 31, 2017 at 6:51
  • 1
    There are other cases where phonology affects the spelling of a morpheme, but I can't think of any others where it occurs between words. For example, words that end in "ch" can be pluralized with "es" or "s" depending on if the "ch" is pronounced as /tʃ/, or something else like /k/ or /x/. An example word with both pronunciations, and therefore both spellings, is conchs/conches.
    – herisson
    Jan 31, 2017 at 6:52

1 Answer 1


The rule is painful as far as code is concerned because the choice between 'a' or 'an' is based on whether it sounds like a vowel is at the start of the word rather than the actual spelling.

For example, as mentioned in a similar question: "A united states citizen, a unique opportunity but an uncle"

This means that any code needs to determine what the word sounds like ... or the equivalent there of (such accessing a mapping table or list of exceptions)

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