Grammar question: "an historic event"?

A well known grammar rule says that we should use an before vowel sounds; for example, an accident, an item, an hour. We use a otherwise: a book, a hotel, a university.

Notice that we say an hour, not a hour. The choice of a or an is based upon the sound of the word, not the spelling. Hour sounds as if it starts with a vowel sound (ow); hence, we use an.

Following this rule, we would say a historic, not an historic because (for most speakers) historic doesn't start with a vowel sound.

Words of three or more syllables that start with h are treated differently by some speakers, though. (This may be because of the tendency of some regional accents to drop initial Hs.)

Here's another example. Which of these pairs of sentences sounds better to you?

We can't agree on a hypothesis.

We can't agree on an hypothesis.

A quick bit of Googling reveals that — as of December 2008 — the phrase a hypothesis is used on 2.22 million pages (80%), and an hypothesis on 538,000 pages (20%). Similarly, a historic gets 70% of the popular vote, and an historic only 30%.

There is a clear preference on the web in favour of a hypothesis and a historic. Even so, a significant minority uses the other form. This supports the view that both forms are widespread. Which form you use seems to be little more than a personal preference and perhaps a matter of accent.

In summary: A historic is more common in online writing, but both usages are sufficiently common to be considered correct.

It all comes down to the sounds, not the letters themselves. Look at (actually, listen to when others say them) the ways that words 'history' and 'historic' are pronounced. Although they are obviously from the same source, there is a major difference in pronunciation - an accent shift. It's HIStory, but it shifts to hisTORical.

Since the HIS- is the accented syllable, the 'H' is firmly pronounced, and you'll never (at least I hope so) hear anyone say 'an history.' With the his-, it's quite a bit different. The syllable is not stressed,and the 'h' sound is much diminished; with some speakers, it fades into oblivion and those speakers naturally and properly use an 'an' before a word starting with 'his-'. We do the same thing every day with 'honor' and 'honest' - It's an honor to meet an honest man.

Speakers are split on this. Some retain enough of an 'h' sound to use 'a' before 'his-, but other dialects have gone to 'an' in that position. The trend has been toward using 'an' more and more, and this may eventually become standard English. Currently, the 'a' is used in formal English, but realize that 'an' is used frequently and is gaining on 'a.'

I've never heard anyone say that, but it's not correct. You're right that you use 'an' before a vowel, but remember that you also use it before a vowel sound, like when you say, "an hour."

As far as I know, it is a hold-over from the days when an initial "h" was silent.

It's weird, though, because we say

"an historic event"

but

"a history book."