Do you write 'an' historic house or 'a' historic house?

Answer 1

I say 'an historic house', so that's how I write it. The general rule is that you use 'an' before a following vowel sound. Notice that it's the sound that counts, not the spelling. For instance, it's 'an honor to meet you', because 'honor' is pronounced starting with the vowel [a], even though it is spelled starting with the consonant 'h'.

Now before the noun 'history', which starts with the sound [h] and the letter 'h', you use 'a': 'a history of spam'. But in the adjective 'historical', the main stress has been shifted to the right onto '-tor-', and this leaves the first syllable 'his-' with no stress. A sound [h] is generally lost from the beginning of an unstressed syllable in English. So, even though 'history' starts with a consonant sound (the [h]), 'historical' starts with a vowel sound ([i]), because the [h] sound was lost, even though the letter 'h' is kept in the spelling.

I know that's complicated, but it gets a little worse. The dropping of the [h] sound in 'historical' is sort of optional. Depending on speaker and style, the [h] might or not drop. In my own pronunciation, oddly enough, it doesn't make any difference as to whether preceding 'an' is used -- it is used even when [h] is still there. However, I can well imagine that some speakers of English who do not drop the [h] of 'historical' can use 'a', rather than 'an', before the [h] here. (Not me, though.)

Answer 2

Both are correct, but it is more common to use 'a' before words that start with a silent 'h', such as 'historic'. So, it would be 'a historic house'.