"An historic." The rule is that you use "an" before a vowel sound and "a" before a consonant sound. "It is an honor." That H is silent. "He is a Hispanic." That H is pronounced. I don't know any Americans who pronounce "historic" as "iss-TOHR-ic". (If so, do they also pronounce "historian" clipped? What about "hypothesis"?) And yet some insist on using "an historic" in writing, because, I don't know, it sounds more pretentious or something. I'm a fan of language changing with the times. I could less care about split infinitives. And I start sentences with prepositions all the times. But language changes like that are a matter of style , while certain things -- like its/it's -- are just matters of being wrong . (Sometimes a subtle distinction, but I warned you this was a pet peeve.) "An historic" is wrong . (Further reading: http://www.wsu.edu/~brians/errors/anhistoric.html , http://www.theslot.com/a-an.html )