is "an historic" somehow grammatically correct?

You can say "an" before a word starting with a sounded "h" if the first syllable of the word is not stressed.

If it is the second syllable which is stressed, you can use "an".

It's optional, though.

an hisTORic event

a HIStory of events

an hoTEL in the city

a HORRible accident

an horrIFic accident

.

"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 like 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.)

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

It depends on whether or not your pronounce the "h" in "historic". Proper grammar requires that you use "an" before words starting with a vowel.

Yes but it's really stuck up.