It is a traditional rule of English that an can be used before words that begin with an H sound if the first syllable of that word is not stressed. Indeed, some traditionalists would say it must be used before such words. Since the first syllable of historic is unstressed, it is acceptable to use an before it.
Also question is, what is the difference between A and an?
So, in other words, if I say "I saw a cat" it means that you and I don't already know what cat I'm talking about. As far as the difference between the two, the only difference is that "a" is used before words that start with a consonant sound and "an" is used before words that start with a vowel sound.
Is it an MBA or a MBA?
It is - an MBA. When the letter M is pronounced, it sounds like "em" so since it begins with a vowel sound and we are saying the letters one by one, I would say "an" MBA.
Where is the used?
The is used to describe a specific noun, w hereas a/an is used to describe a more general noun. For this reason, the is also referred to as a definite article, and a/an is referred to as an indefinite article. The definite article, the, is used before both singular and plural nouns w hen the noun is specific.