Cambridge: a university / an university?
You were probably taught at school ‘an’ should be followed by a vowel (a,e,i,o,u) and a should be followed by a consonant:
Unfortunately, this is not always true!
When to use an or a depends on how the word is pronounced and not on how it is written.
The U in university is pronounced with a long ‘u’ sound which sounds like ‘yew’ and is written as j in the phonetic alphabet. So, although the letter is a vowel, it is not pronounced like one in 'university' because it does not have a vowel sound. We therefore say ‘a university’.
The U in umbrella is pronounced as a vowel sound ( Λ using the phonetic alphabet) and so we use ‘an’. We therefore say ‘an umbrella’.
This rule also applies to the use of consonants.
The word hour has a soft ‘h’ which is weakly pronounced and therefore we say ‘an hour’.
If the word has a hard ‘h’, like house, we use ‘a’ (a house).
Take a look at the following words and decide if they should have ‘a’ or ‘an’