here are a couple copy/paste examples from a couple sites that explains my understanding:
grammar.quickanddirtytips.com/a-historic-versus-an-historic.aspx
"the choice between "a" and "an" is governed by the first sound of the next word. if it's a consonant
sound, choose "a"; if it's a vowel sound, choose "an." although there are regional variations, the
standard american pronunciation of "historic" starts with a consonant sound (just like the
words "hit," "hipster," and "highlighter"), so the correct choice is "a historic." there's nothing special
about "historic" that exempts it from the standard rule.
oxforddictionaries.com/words/a-historic-event-or-an-historic-event
a historic event or an historic event?
people often believe that they should use the indefinite article an in front of words like historic, horrific,
or hotel. are they right or wrong? should you say
