ARTICLES

First the good news:There are only three articles in English: a, an and the.

There are two types of articles indefinite 'a' and 'an' or definite 'the'. You also need to know when not to use an article.

The bad news is that their proper use is complex, especially when you get into the advanced use of English. Quite often you have to work it out by what sounds right, which can be frustrating for a learner.

INDEFINITE ARTICLES - A AND AN (DETERMINERS)

A and an are the indefinite articles. They refer to something not specifically known to the person you are communicating with.

A and an are used before nouns that introduce something or someone you have not mentioned before:-

For example

"I saw an elephant this morning." 

"I ate a banana for lunch."

A and an are also used when talking about your profession:-

For example

"I am an English teacher." 

"I am a builder."

You use a when the noun you are referring to begins with a consonant (b, c, d, f, g, h, j, k, l, m, n, p, q, r, s, t, v, w, x, y or z), for example, "a city", "a factory", and "a hotel".

You use an when the noun you are referring to begins with a vowel (a, e, i, o, u)

Pronunciation changes this rule. It's the sound that matters, not the spelling. 

Note! If the next word begins with a consonant sound when we say it, for example, "university" then we use a.

If the next word begins with a vowel sound when we say it, for example "hour" then we use an.

We say "university" with a "y" sound at the beginning as though it were spelt "youniversity".

So, "a university" IS correct.

We say "hour" with a silent h as though it were spelt "our".

So, "an hour" IS correct.