Both occur, but "a historic" is standard choice in modern English.
Since most speakers pronounce the h, it takes "a" not "an".
Contrast to "an hour", where the h is silent.
Both occur, but "a historic" is standard choice in modern English.
Since most speakers pronounce the h, it takes "a" not "an".
Contrast to "an hour", where the h is silent.
And for 'herb' it depends on which dialect of English you speak.