I have read that the the modern 'an' derives from the Old English 'ān', which is also the source of 'one'. So I guess I can see how "one hour; one apple" could work, but that doesn't explain 'why'. What is the function of having one indefinite article for words starting with consonant sounds, and another of words starting with vowel sounds? I did some searching around but the entries I found cited when you use should 'a' vs 'an' but not the why.

  • 2
    The first article I came across on a Google search, ef.com, has: 'In English, the two indefinite articles are a and an. Like other articles, indefinite articles are invariable. You use one or the other, depending on the first letter of the word following the article, for pronunciation reasons. [emphasis mine] There are two ways of pronouncing 'a', neither of which would go well before 'apple'. There are three ways ... Oct 22, 2016 at 15:30
  • of pronouncing 'the' - unmarked, stressed, and the one used before a vowel. But one spelling covers all three pronunciations adequately, there being no n-sound etc. Oct 22, 2016 at 15:31
  • 1
    Basically, people trip over their tongues when they try to do it the "wrong" way.
    – Hot Licks
    Oct 22, 2016 at 22:12

2 Answers 2


Linguistic changes, including sound changes, come naturally. There’s no function for having two forms of the indefinite article. This is probably not the answer you’re looking for, but it is so because it is so.

As for the “why”, linguists are also not 100% sure, but many point to the principle of least effort. One of the most common effects of this principle is cluster reduction: perhaps for most people it’s easier to pronounce a man than an man, whereas an hour doesn’t contain a cluster to be reduced.

  • 2
    It's also worth noting that this sort of thing appears in many languages. Latin has 'a / ab' meaning 'from, by', where 'a' is used before consonants, and 'ab' before vowels. Similarly, Classical Greek has 'οὐκ / οὐ', meaning 'not' where, once again, 'οὐκ' is used before vowels, and 'οὐ' before consonants.
    – Socrates
    Oct 22, 2016 at 20:01

There are not two different indefinite articles. Both a and an have the same origin; but before a consonant the /n/ has been lost — much like the /v/ in of in ordinary speech.

Not the answer you're looking for? Browse other questions tagged or ask your own question.