I found your site as I was searching for an answer to my question.
I have used the vowel sound of the following-word rule in order to determine whether to use an 'a' or an 'an' in a sentence. On your site, I found you felt the same. This leads me to my question...
Given the vowel sound rule, why is it acceptable to use AN in front of the word historic? I suspect it's a barnacle from older English and is proper, but it always sounds off when I hear it.
When pronouncing the words 'historic' and 'historical', the accent falls on the second syllable, and many pronounce them as starting with a vowel. For those people, it is appropriate to use 'an' before 'historic' and 'historical'. Therefore, you have a choice depending on what sounds best for you. There is a lot of leniency on this issue. If you're still unsure, opt for 'a historical' and 'a historic' as these remain preferable - especially in formal writing.
