My phonology professor went on about this endlessly. In short, what we write as "h" is, in practice, a voiceless version of whatever vowel follows it - try saying the words "house", "hair", "hear" and so on, and notice the way your mouth shapes itself before you start to speak; hold it, and then alternate between voicing and not-voicing (that is, vibrating vocal chords - an easier example of that is to hiss "sssssssss-zzzzzzzzz-sssssssss-zzzzzzz" and feel the difference in your throat).

Sorry, I ramble. I like that subject. Anyway, point is, in practice people often drop whatever half-formed sound there is that tries to be an "h" in the first place, and so we use "an", but that's only verbal. In writing - at least until our writing system changes to reflect spoken language, again (and becomes even MORE complicated, *sigh*) - you always need to use the "a". It'll look wrong on paper otherwise.


...I've gone lecture-y again, haven't I? Sorry. But I hope that helps.

Depends on whether you follow that the H is silent or not. It can make a difference, but its totally up to your style or how you were taught.

It has to do with whether the next word has a vowel sound, not letter. So it would be "a historian" or "an 'istorian." In writing, it would probably depend on whether you wrote out the accent.

I'm pretty sure that a/an depends on the first pronounced sound of a word. Since you leave off the initial h when speaking, you should probably use "an" when talking to someone, but I would use "a" when writing. That's just my opinion, though, and might not be the correct usage.