Flammable vs Inflammable – What’s The Difference?

Flammable and inflammable cause a lot of confusion. How do we know when to use which? Fortunately, I have an easy way to remember the difference.

Are you ready?

There isn’t one. 

Flammable, Inflammable; Tomato, Tomahto

That’s right, flammable and inflammable mean the same thing: capable of being set on fire. 

But they look like opposites, so how can this be? And what word do you use if you want to say that something isn’t flammable?

Well, fire marshal Michael is here to put out all your burning questions. 

In the article below, I’ll throw water on your confusion, explain why it’s cool to use flammable instead of inflammable (even though they mean the same thing), and introduce you to our hot new friend: nonflammable.

Ready? Let’s get fired up!

Smoke Gets in Your Eyes — Why Flammable and Inflammable Look Like Opposites

Flammable and inflammable look like opposites because of our associations with the prefix “in-.” We often think of in- as meaning “not,” like the prefixes un- or non-. Because sometimes it does mean that! But it can also mean “in” or “into.”

When we look at a word like inflammable, we instinctively feel it must be the opposite of flammable. And for good reason. Many familiar words act this way, because in- often means “not.”  

For example, when something is not complete, we say that it’s incomplete. If an answer isn’t valid, it’s invalid. And your bank funds? Well, they can either be sufficient or…yeah, you know — insufficient.

I could go on and on with this — you’re probably thinking of a few more examples right now. But on the other hand,  in- can also mean, well, “in,” or “into,” and that’s what’s going on with inflammable.

Clearing the Smoke — Why They’re Not

Many words in English contain this in/into usage of in-. 

If we have an insight, for example, it doesn’t mean that we cannot see, it means that we can see into. When we are invigorated, we feel vigorous, literally, “in vigor.” The common word input provides the best example I can think of. When we input data, for instance, we literally put the data in.

Our word inflammable, it turns out, is derived from the Latin word inflammare, from which we also get the word inflame, which means to set on fire — literally, “in or into flame.”

So this is why something that’s flammable equals inflammable. 

Simply put, flammable is a bit like saying flame-able. That is, it could catch fire, turn to flames. Inflammable, similarly, is a bit like saying inflame-able. That is, it could catch fire, turn to flames.

(Do I hear an echo?)

So, if these words mean the same thing, you can use them interchangeably, right? Problem solved, case closed.

Hold on! Just cool your jets, hot stuff.

Use Flammable If You Want to Look Cool

It appears, according to sources like the Oxford English Dictionary, that the word inflammable has been with us longer than flammable, but they’ve both been lighting up the language for the last couple of centuries, and pretty much interchangeably.

However, in the case of Flammable v. Inflammable, the court of public opinion has ruled: Flammable in, inflammable out. Over the years, the flammable/inflammable confusion has led many to prefer flammable, particularly when it comes to safety guidelines and instructions. 

Regulators and manufacturers of various products throughout the 20th century noticed that people were taking inflammable to mean not flammable, precisely because of the frequent negative meaning of the in- prefix we discussed earlier.

So, perhaps I, too, should recommend that you choose flammable, and allow inflammable to fizzle out. Especially if you’re writing instructions, safety information, or anything technical, this is the best way to go.

So that’s cleared up — but what if something isn’t flammable? 

The Opposite of Flammable — Nonflammable, the Hot New Thing

Well, here is a word that actually makes sense: Nonflammable.

And yes, it means what it looks like it means. If it’s nonflammable, it won’t catch fire. It’s un- flammable, if you will. Not – flame – able.

Now doesn’t that just set your heart on fire?

Nonflammable seems to have joined the English language in the 19th century, when writers thought that they needed a clearer opposite to flammable. (And I think they were right!) 

A little warning: You may see a few folks who want to stick a hyphen in there: non-flammable. Others, like your computer’s spelling and grammar checker, perhaps, suggest a space: non flammable. But most dictionaries prefer the non-hyphenated version, and I do too. To be on the safe side, though, always check with your organization’s style guide or the trend in your field.

Flammable, Inflammable, and Nonflammable Used Correctly

Just to make sure all our hard work doesn’t go up in smoke, let’s look at a couple of examples.

Flammable and Inflammable Used Correctly

In the examples below, flammable is preferred, to avoid confusion. However, inflammable is also correct.

“When toasting marshmallows, be careful using wooden sticks, as wood can be flammable (or inflammable).”

“Some hair sprays are flammable (inflammable), which is why you should never use them near an open flame, such as a candle.”

Nonflammable Used Correctly

In these examples, only nonflammable is correct.

“Mosquitos just eat me alive, but luckily Ariel brought a nonflammable insect repellent that’s safe to use at the campfire.”

“The firefighter’s gear is made from nonflammable materials for their protection.”

Now We’re Cookin’ with Gas

I hope you’re stoked to get out there and set the world on fire with your new knowledge flammable, inflammable, and nonflammable. And if you’re in the dark about any other common English confusions, the EditorNinja blog has a whole slew of articles to light your way, with more content coming every week. 

It’s pretty lit.

A Brief Lesson in English Language History — The Latin Connection
You see, English is basically a dumpster fire of a language. And into this burning trash heap has been thrown a whole lot of Latin, coming into our language at many different times from many different places. 
In 1066, for example, when English sounded like German — but even worse — England was invaded by the French (they went by “Norman” back then). The French language was derived from Latin, so when French words started mixing into English, we gained a wealth of Latinate words. 
At other times, scholars just grabbed whatever Latin they needed and threw it into the flaming heap of English when they felt like it. 
So what does this mean for us? Well, two things in particular: 
For one, this is why we have both flammable and inflammable in our language: they were brought in at different times. And for another, English took the prefix in- from Latin — not just attached to the word inflammable, but as a unit that can be attached to thousands of other words.
Furthermore, for some reason, in- already had two meanings: in some cases, it meant “not” or “against,” as it does in inactive, and in other cases “in” or “into,” as it does in ingest. Thanks, Latin.

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