When describing unspecific singular nouns (person, place, or things) or noun phrases, we use “a” or “an” to replace the word “one”. By replacing the word “one”, we eliminate the emphasis of quantity and focus on the noun itself.

I have one company. (“company” is the noun)

He has one dog. (“dog” is the noun)

They have one house. (“house” is the noun)

There is one hour left. (“hour is the noun)

Our hometown has one high school. (“high school” is the noun phrase)

The movie had one unicorn. (“unicorn” is the noun)

 

Replacing “one”

Generally speaking, if the noun begins with a vowel or sounds like it starts with a vowel, use “an”, otherwise use “a”.

Vowels

A

E

I

O

U

(Mnemonic to remember vowels: “Adam, Eve, I Owe U”)

Exceptions:

USE “A”

1. The letter “u”: If a word starts with “u” and is pronounced like “you”, then use “a”. For example, the word “unicorn” is pronounced like “YOO-NI-KAWRN”, so you use “a” to make “a unicorn”.

a unicorn

2. The letter “o”: If a word starts with “o” and is pronounced like “w”, then use “a”. For example, the word “one” is pronounced like “WON”, so you use “a” to make “a one-eyed pirate”.

a one-eye pirate

USE “AN”

3. The letter “h”: If the “h” is silent at the beginning of a word and you only hear the vowel sound, then use “an”. For example, the word “honor” is pronounced liked “ON-ER”, so you would use “an” to make “an honor”. However, the word “horse” is pronounced like “HAWRS” (which has an “h” sound), so you should use “a” to make “a horse”.

an honor a horse

What about using “the”?

“The” is a definite article. It is used when you are referring to a specific noun that you can picture in your mind. We use “a” and “an” only when we are speaking about unspecific things or things that we cannot picture in our mind.

Examples:

He has a dog.

All you know is that he has some kind of dog. You don’t know which kind or any specific information about that kind of dog. It’s just a random dog. It could be tall, short, skinny, or fat. You don’t know. Thus, you can’t say he has “the” dog. There’s not enough information given to say that. However, you can say the following:

“The golden retriever that is standing next to him is his dog.”

Here, you know the specific kind of dog he has. You can picture this kind of dog in your mind.

Blast to the Past

Now, let’s replace our sentences using “a” and “an”.

I have a company. (“Company” begins with “c”. “C” is not a vowel, so we use “a”.)

He has a dog. (“Dog” begins with “d”. “D” is not a vowel, so we use “a”.)

They have a house. (“House” begins with “h”. “H” is not a vowel and is NOT silent in this word, so we use “a”)

There is an hour left. (“Hour” begins with “h”. “H” is not a vowel, but it IS silent in the word “hour”. “Hour” is pronounced like “OUR”, so we use “an”.)

Our hometown has a high school. (“High school” begins with “h”. “H” is not a vowel and is NOT silent in this word, so we use “a”). The movie had a unicorn. (“Unicorn” begins with “u”. “U” is a vowel, but it is pronounced like “YOU”, so we use "a”).

Bonus sentence:

There was _____ one-eyed monster in the closet.