Which convention? ‘An hotel’ has largely been superseded by ‘a hotel’, but I would say "a history book" but "an historic event."
Guess it’s your choice. 😊
I thought the 'an' business was because we used to pronounce hotel without an aspirated H, more like the French pronunciation?
I don't believe it was ever a convention to use an before a naturally aspirated h was it? We would never say things like "I'd like to buy an Harp", or "Here comes an horde of Vikings" but you're right, there does seem to be a common exception in the specific case of an historic event.