hmm ... not sure how clear I was in that last posting. I meant that when 'h' is pronounced at the beginning of a word - as it is in nearly all cases - then the general rule will be to use 'a' - as with other consonants. There are a few Latin words which have 'h' as a silent letter - hour / honour etc - so those use 'an' because the words begins with a vowel sound. The only complication is in the cases I mentioned above of a few 'his ...' words where the 'h' is sometimes pronounced so weakly as to lead to some variation between 'a' and 'an'.