Idiom vs. Metaphor: How to Recognize the Difference

Both idioms and metaphors are forms of figurative language, which are non-literal ways to make your writing more interesting. However, idioms are well-known expressions that make a point different than what they actually say.

Examples of idioms and what they mean include:

• I got cold feet before the wedding. (I got too nervous to go through with the wedding.)
• It's raining cats and dogs outside. (It's raining a lot outside.)
• That computer is as dead as a doornail. (That computer is totally dead.)

You've probably heard these expressions and others like them many times. Idioms are colloquial ways to say something that wouldn't make sense to someone who wasn't familiar with the language. Saying that it's "raining cats and dogs" would be very confusing to an English learner who had never heard that idiom before.

A metaphor is another form of figurative language. Like similes, metaphors compare two things that share one characteristic but aren't alike otherwise.

Examples of metaphors and what they're comparing include:

• The night sky was a blanket of stars. (compares the covering of night with the covering of a blanket)
• You are such an angel for helping me out. (compares your kindness with the kindness of an angel)
• This decision is really weighing on my mind. (compares the emotional weight of the decision with the physical weight of something heavy)

Like idioms, metaphors aren't literal. They are often used as poetic devices to make a poem more vivid. Extended metaphors are more complex versions of metaphors, and they can also occur in both fiction and poetry.

So if both are figurative and not literal, what's the difference between idiom and metaphor? The biggest difference between idioms and metaphors is how they are used. Idioms are almost nonsensical expressions, while there is a clear comparison in a metaphor.

Simply put:

• Idioms are used to make a point in a colloquial way.
• Metaphors are used to compare two things.

For example, describing a rainy day as "raining cats and dogs" is an idiom, not a metaphor, because it's not comparing rain to anything that makes sense. It's just an expression that means "raining a lot." A metaphor that describes a rainy day would be "The sky is a weeping child."

Other examples include:

• Idiom - Marcy has a green thumb in the garden. (Marcy is talented in the garden.)
• Metaphor - Marcy lovingly tends her babies in the garden. (Marcy treats the plants in her garden as gently as someone would treat babies.)

• Idiom - The principal caught us red-handed. (The principal caught us doing something wrong.)
• Metaphor - The principal's eyes were a glaring light on our actions. (The principal's judgment was like a bright light on us.)

• Idiom - A little bird told me the good news. (I heard that there is good news.)
• Metaphor - The good news floated down the river of our social circle. (The good news traveled like something would travel down a river.)

• Idiom - My dad's been on cloud nine since his team won the game. (My dad has been overjoyed since his team won the game.)
• Metaphor - My dad is glowing since his team won the game. (His excitement is as bright as a light.)

As you can see, metaphors tend to sound more poetic than idioms. Idioms are more common in everyday speech, while metaphors are a more effective way to compare concepts in writing. Writers sometimes lean on idioms because they're so well known. However, using too many idioms and not enough metaphors can make a writer sound clichéd.

If you can think of a few exceptions to this rule, there's a good reason. Some metaphors have become so well known that they have practically become idioms themselves.

For example:

• Owen is the black sheep of his family. ("Black sheep" compares a sheep that doesn't fit in with their flock with a person who doesn't fit in with their surroundings.)
• You can ask me anything; I'm an open book. ("Open book" compares a book that's easy to read with a person who easily provides information.)
• My nephew is a late bloomer. ("Late bloomer" compares a flower that blooms late in the season with a person who is late to develop.)
• Nathaniel is drowning in paperwork this week. ("Drowning in paperwork" compares being overwhelmed by water with being overwhelmed by paperwork.)
• The baby's laugh is music to my ears. ("Music to my ears" compares the sweetness of music to the sweetness of the baby's laugh.)

You may think these common expressions are idioms, but they're not. Because they function to compare two things, they are simply very common metaphors.

English has thousands of common idioms and millions of ways to use metaphors. Now that you know the difference between metaphors vs. idioms, you're likely to notice them everywhere you go! For more help on idioms, check out 100 American idioms to test your knowledge.