When they first learn English, many are taught that we simply use the article a before countable nouns that start with a consonant and an with countable nouns that start with a vowel. It’s actually slightly more complicated than that, so read on about the tips below and you’ll soon know exactly when to use each.
To make the rules a little bit clearer, we use a before adjective / adverbs and countable nouns with a consonant sound. And an before adjectives / adverbs and countable nouns with a vowel sound. The key here is the word sound. Just because a word starts with a consonant, doesn’t necessarily mean that it has a consonant sound.
Take a look at the following word: Hour
As you can see, it starts with a consonant letter. But when you actually produce the word, it is a vowel sound /aʊər/ that comes from your mouth. Therefore, you would use the article an and not a.
Let's see another example: Euro
This word starts with a vowel letter, but you produce it with the consonant sound /j/. Thus, you would use the article a and not an.
Normally, it’s pretty easy to tell the difference and for the most part the traditional rules apply. But if you’re ever unsure, just create the sound and decide for yourself whether it is a consonant sound or a vowel sound you are producing.