"Diffuse" Versus "Defuse"

And “convince” versus “persuade.”

Rob Reinalda, Writing for
3-minute read
Episode #193

Some pairs of words are used interchangeably, even indiscriminately. Often the words in question sound similar, and that creates confusion. Other times they are simply misused so frequently—owing to their similarity of meaning, despite a nuanced difference—that the misuse becomes commonplace. 

Today, we’ll look at two pairs. 

Convince Versus Persuade

First, consider the verbs “convince” and “persuade.” Even though the adjective forms —“convincing” and “persuasive”—are synonyms, the verbs “convince” and “persuade” should be used in different contexts.

Frequently, you might hear someone say something like, “I convinced Melvin to make his presentation less tedious.” Well, you may have succeeded in getting Melvin to spice things up, slide-wise, but what you actually did is “persuade” him to do so. (You may also have “convinced” him that it would be a splendid idea for his convinceaudience not to be lulled into a vapid stupor.)

Here's the key difference between the two words. A person persuades another to do something, to take action. “I persuaded Algernon to go with me to the roller derby.” Because “to go” is an action, the correct verb choice is “persuade."

Then there is this sentence: “I convinced Algernon that roller derby is an enthralling way to spend a Saturday.”   In that case, there's a concept, an idea, or an opinion at stake. That’s when “convince” is the way to go.

You persuade someone to take an action, and you convince them that your idea is a good one. 


You persuade someone to take an action, and you convince them that your idea is a good one.

The Tip

The Quick and Dirty Tip is an easy mnemonic device. The second syllable of each word holds the key. Let the “a” in the last syllable of “persuade” stand for “action”, and use “persuade” when you want someone to take action. Let the “i” in the last syllable of “convince” stand for “idea,” and use “convince” when you are conveying an idea.  

With luck, we have convinced you that this distinction is important and have persuaded you to get it right.

Defuse Versus Diffuse

Now, on to “defuse” and “diffuse.” These verbs are nearly homonyms; they sound almost identical. Their meanings differ, however. Here’s how they differ, along with how to keep them distinct in your discourse and your writing. (Remember, proper enunciation helps ensure your meaning is communicated.)

According to Dictionary.com, which cites Random House, “defuse” means “to make less dangerous, tense, or embarrassing [as in]: to defuse a potentially ugly situation.” That’s definition number two. The primary definition is more to the point, and more literal: “to remove the fuse from (a bomb, mine, etc.).” De-fuse.  

Aardvark and the peeves were at each other's throats. Squiggly knew he had to defuse the situation quickly.

The same sources state that “diffuse” means “to pour out and spread, as a fluid; to spread or scatter widely or thinly; disseminate.” 

It has another meaning, in physics: “to spread by diffusion”—the movement of objects or particles away from one another. Think of “diffused light,” which spreads into a haze rather than holding to a concentrated beam of light. 

The light diffused through the room.

 Also, “diffuse” is the opposite of “fusion,” which means a coming together of elements. So diffusion is the spreading apart of elements.

The Second Tip

You can keep “defuse” and “diffuse” straight by talking like someone with a strong New Jersey accent a minute. Use defuse when you are removing “de fuse” from an explosive situation—remove “de fuse.”Otherwise, it could blow up, and everything in sight would be diffused in an instant. 

This podcast was written by Rob Reinalda, executive editor for Ragan Communications (word_czar on Twitter), and I'm Mignon Fogarty, the author of The Grammar Devotional and Grammar Girl's Quick and Dirty Tips for Better Writing.


About the Author

Rob Reinalda, Writing for Grammar Girl

Rob Reinalda, winner of ACES' 2019 Robinson Prize for excellence in editing, is the founder and principal of Word Czar Media