It is common to use
1a an historical event
2a an hotel
rather than
1b a historical event
2b a hotel
Why 'an' is used in such case?
It is common to use
1a an historical event
2a an hotel
rather than
1b a historical event
2b a hotel
Why 'an' is used in such case?
"An" is used before a vowel sound. "A" is used before a consonant sound.
The usual pronunciations of "hotel" and "historical" sound the h, so those words begin with the consonant sound [h], so it's "a hotel" and "a historical ...".
However, some people used to pronounce "hotel" with the h silent. The word is derived from a French word where the h is silent. So some people used the French pronunciation. But now it's much more common to pronounce "hotel" the English way, with a sounded h.
Google Ngrams shows that, in British English, "a hotel" didn't overtake "an hotel" until 1931, whereas in American English, "a hotel" had overtaken "an hotel" by 1820. (These stats should be taken with a grain of salt, just like any Ngrams data brought to bear on a matter of spoken English; written English tends to lag spoken English.)
Why would some people say "an historical ..."? In some people's accents, the h sound is dropped in some circumstances. This is more likely to happen if the h sound is in a weak (unstressed) syllable. The first syllable of "historical" is weak, and so we get "an 'istorical". People with that accent feature might also "an 'orrific".