This is an attempt to sort out the spelling and pronunciation of nouns and adjectives that begin with ‘h’ and, more crucially, the form of the indefinite article that should be used with them.
There are some words of French origin in which the initial /h/ is not sounded. They include ‘heir’, ‘honour’ and ‘hour’. There is no difficulty with these. They are pronounced /ɛə(r)/, /ˈɒnə(r)/ and /aʊə(r)/, and so are preceded by ‘an’. Words beginning with a sounded /h/ can be divided into three groups, (1) those of one or two syllables, (2a) those of three or more syllables in which the first syllable is stressed and (2b) those of three or more syllables in which the second syllable is stressed. Stress is indicated in what follows by underlining.
Words in the first group are normally preceded by ‘a’. They include ‘hotel’, ‘hostel’, ‘host’, ‘hearty’, ‘hero’,’hardy’ and many more. ‘Hotel’ is exceptional in two ways. The first is that pretentious speakers may not pronounce the initial /h/, perhaps thinking thereby to sound more French, and consequently more educated and sophisticated. The second, and more interesting, point is that the stress in ‘hotel’ falls on the second syllable. It is probably the only two-syllable word starting with ‘h’ in which that happens, but counter-examples would be welcome.
Words in group (2a) include ‘history’, ‘herbalist’, ‘heightening’ and ‘helicopter’. These are always preceded by ‘a’. They contrast with words in group (2b), which include ‘historian’, ‘historical, ‘hiatus’ and ‘Hibernian’. It is here that uncertainty arises. There is a tendency among native speakers, including this one, (and I have noticed, that admirable commentator on current affairs, Andrew Marr) to use ‘an’ before words in this group.
We are of course free to pronounce words however we like, but how should we write the indefinite article when it occurs before words in group 2(b)? ‘The Cambridge Guide to English Usage’ is in no doubt. The initial ‘h’ (except in words those such as ‘heir’, ‘honour’ and ‘hour’ in which it is never pronounced)
may have been silent or varied in earlier times, leaving uncertainty as to whether an was required or not. But their pronunciation is no longer variable and provides no phonetic justification for an. Its use with them is a stylistic nicety, lending historical nuances to discourse in which tradition dies hard.
I have the greatest respect for the Cambridge Guide, and it gives me no comfort to disagree with it, but in this one instance it ignores the crucial question of stress. The general guidance on a/an is that the choice between them should reflect pronunciation and not spelling. So I, at least, will write, when I have to, ‘a history book’, but ‘an historical discovery’.