Question: Why do we say a union and not an union? Why do we say an MBA when MBA starts with a consonant?

Grammar:

Indefinite Article

The general rule for indefinite articles (a or an) is:

* If the next word starts with a vowel (a, e, i, o, u) then use an.

* In other cases, use a. However, the more accurate rule is:

* If the next word starts with a vowel sound, use an.

So for example, MBA doesn’t start with the /m/ sound. It starts with /em/, and /e/ is a vowel sound. Therefore we write an MBA. The word union may start with U, but when you pronounce it, it actually starts with a Y sound, or /j/. This Y sound is not considered a vowel sound, and so you should say a union.