In elementary school, most of us learned that it is proper to use “an” before a word that begins in a vowel. Otherwise, use “a”. However, the English language has exceptions to every rule. This is no different. For example, “an hour” is proper as opposed to “a hour”. So why do we come across “an historic” when historic begins with “h”? Don’t we all pronounce the “h” in historic? Sort of. “H” is a weak consonant and pronounced differently across the world, which affects our choice of indefinite article (a or an).
Is there an answer? Yes. Historic is correctly pronounced with the “h” and therefore requires “a” before it. So, the correct pairing of words is “a historic.”