Here's how to determine which one to use:
"A" is used before:
* Consonants:
- A cat, a dog, a house, a book
* Words that begin with a vowel sound, even if the first letter is a consonant:
- A university, a European, a one-way street
* Abbreviations that start with a consonant sound:
- A UFO, a VIP, a NATO member
"An" is used before:
* Vowels:
- An apple, an egg, an orange, an umbrella
* Words that begin with a silent "h":
- An hour, an honest man, an heir
* Words that begin with a vowel sound, even if the first letter is a vowel:
- An honour, an MP, an X-ray
Why do we use "a" and "an"?
The use of "a" and "an" comes from the historical development of the English language. Originally, the word "an" was a separate word meaning "one." Over time, it became merged with the indefinite article "a" before vowel sounds.
Remember:
* "A" and "an" are used only with singular countable nouns.
* They are not used with plural nouns or uncountable nouns.
Examples:
* Singular countable noun: "I saw a bird."
* Plural noun: "I saw birds."
* Uncountable noun: "I drank some water." (No article needed)