When to use A or An: Sound vs Spelling 

Using an and a does not depend on the spelling of the word it comes before, it depends on the pronunciation of the word. In most cases though, an is used before words that begin with vowels (a, e, i, o u.): 

an apple 

an elephant 

an igloo 

an oven 

an umbrella 

If a word starts with a consonant sound, use a. 

a ball 

a car 

a doll 

Vowel Sounds

It is very important to know that when a word starts with a vowel sound, you should use an. But, sometimes the letter ‘u’ is pronounced as ‘yu’. Try saying these two words, see if notice how the ‘u’ is pronounced in two different ways. 

an unforgettable experience – the ‘u’ in unforgettable has a vowel sound so we use an. 

a university – the ‘u’ in university has a ‘yu’ sound so we use a. 

This is also the case with the letter ‘o’, which may sometimes have a ‘wuh’ sound. Compare: 

an octopus – octopus starts with a vowel sound. 

a one-track mind – one-track starts with a ‘wuh’ sound. 

The Silent h

Sometimes with words that begin with h, the h sound is not pronounced. When the ‘h’ is silent, you decide based on the following letter, which is generally always a vowel. Let’s look at an example. 

an honour – the h is silent. We use “an” because the h is not pronounced: (h)onour. 

a historic day – the h is pronounced. Historic starts with an h sound, so we use “a”.