I am reading The Elements of Style and get stuck at the word flammable. There is the statement about the word:

An oddity, chiefly useful in saving lives. The common word meaning "combustible" is inflammable. But some people are thrown off by the in- and think inflammable means "not combustible". For this reason, trucks carrying gasoline or explosive are now marked flammable. Unless you are operating such a truck and hence are concerned with the safety of children and illiterates, use inflammable.

Explanation above shows that flammable and inflammable have the same meaning actually. To avoid the misunderstand, people now use flammable to illustrate the danger, which easily be gotten from the last but one sentence. However the last sentence's meaning is contradictory to this, I think, and some helps or advice are needed here for comprehension. Thanks.

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    Your analysis is correct. The two words mean the same thing but "inflammable" is easily misunderstood. Sensible people, therefore, use "flammable" but the authors of Elements of Style don't want you to be sensible, because... well, I don't know why. Commented Mar 13, 2014 at 14:31
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    I think the quoted text is unnecessarily passive-aggressive about the issue. Especially considering that the majority of times that the word (in)flammable is going to be used is on warning signs where the meaning needs to be clear for safety reasons.
    – nitro2k01
    Commented Mar 13, 2014 at 14:38
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    @SteveJessop Indeed. I wasn't disputing Hellion's answer, but rather commenting on the quoted guideline in general. I do agree that his answer is the most appropriate because it exactly answers what was asked.
    – nitro2k01
    Commented Mar 13, 2014 at 14:43
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    Kind of surprised nobody has posted this yet. “‘Inflammable’ means ‘flammable’? What a country!” Commented Mar 13, 2014 at 16:01
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    In my dialect, I'd call the authors' attitude as displayed in that last sentence "snotty".
    – swbarnes2
    Commented Mar 13, 2014 at 19:11

8 Answers 8


The paragraph says basically that the use of "flammable" is purposely "dumbing down" your language in order to cater to uneducated people, and that is a bad thing, so you should avoid doing it (unless you NEED to do so for some specific reason).


Flammable is replacing inflammable for exactly the reason suggested in that quote. There is no harm in it, flammable works just as well in any context in which you might say inflammable. In my opinion, the last sentence of that quote is unnecessary and I get no heartburn from the idea that flammable will ultimately replace inflammable in the English language. I completely agree with Hellion, his explanation says exactly what the author of the text is trying to say. I just disagree with the final line of the text.

EDIT: By the way, I remember asking that as a kid. "Why does this say that gasoline doesn't burn?" I was prone to experimentation as a kid too. Hmm, good thing I asked! :)

Further EDIT: Great quote from Grammar Girl: "Flammable" and "inflammable" mean the same thing; they both mean "easy to burn." "Inflammable" is the original word, but then in the 1920s, according to Merriam-Webster's Dictionary of English Usage, the National Fire Protection Association started encouraging people to use the word "flammable" instead because they were worried people could mistakenly think "inflammable" meant "not flammable." They saw it as a safety issue. Academics were inflamed (get it?) because they didn't appreciate the Fire Protection Association messing with the language and promoting "corrupt" words. Perhaps they thought dumb people should die a firey death if they went around holding matches to inflammable objects. Regardless, linguists have groused about "flammable" in usage books ever since.

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    +1 I agree when both the words mean same, why use something that creates ambiguity?
    – Maulik V
    Commented Mar 13, 2014 at 5:22
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    Particularly when a misunderstanding could be dangerous. Commented Mar 13, 2014 at 5:44
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    "I get no heartburn"; because your heart is uninflammable or because it's unflammable? ;) Commented Mar 13, 2014 at 11:59
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    Because it's made of stone. Commented Mar 13, 2014 at 12:01
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    I'm copying this here because it is very relevant: Useful to note that (according to Google Ngrams) usage of flammable surpassed that of inflammable in 1971. The Elements Of Style is all very well, but inflammable is clearly on the way out. – benshepherd 5 hours ago -- benshepherd's original link is active on Maulik V's answer. Commented Mar 13, 2014 at 14:39

A good question, indeed.

Here I found something very useful that says...

"Inflammable" is the original word, but then in the 1920s, according to Merriam-Webster's Dictionary of English Usage, the National Fire Protection Association started encouraging people to use the word "flammable" instead because they were worried people could mistakenly think "inflammable" meant "not flammable."

Basically, the prefix in-in inflammable is the Latin preposition which means en-, not un- which is used in negation. Making inflammable flammable makes sense to me as it avoids ambiguity for children and illiterates. Also, literates do know 'flammable' is 'flammable' so using a word that everybody understands is okay.

Here is the list of Latin roots where you find English in and its root en- and *in (negative) and its root un-.


Note that combustible is not the same as (in)flammable:

  • combustible means that a substance can burn or be burned.
  • (in)flammable means that it is easy to start the combustion

While people mix these meanings in everyday language (see below), I find it odd in a text concerned about precision of language.

As a chemist, I'd always use flammable without in - this is unambiguous, which is particularly good for words that are "useful in saving lives"
For the negation, not flammable is unambiguous as well. - This is also the term used in the corresponding regulations.

That being said, there is of course nothing wrong with knowing the foreign roots of terms, how language developed and about false friends (also within one language). But as others have noted, languages do develop.

At least in French and Italian the corresponding words do not differentiate (much) between combustible and the ease of starting the combustion (ignition).
German instead uses "entzündlich" which would literally correspond to ignitable (though that again has a slightly different meaning - German would be "zündfähig"). AFAIK important regulations (including the terms for metioned gasoline truck) are largely influenced by the DIN (German industrial norms) and thus make differentiations which are "natural" in German language and which are of practical importance. After all, the risks associated with a truck full of wood and a truck full of gasoline are quite different. And language is largely about communication (particularly on a lanugage learners site).

  • I almost said (about) the same thing. Inflammable has always meant dangerously so to me. As if flammable meant burnable while inflammable meant explosive. I was pretty sure of my answer, and I then tried to find documentation to back me up. At least in the first 5 references, I couldn't find it. I think the earliest changes took place while we weren't watching. Commented Mar 13, 2014 at 12:34
  • When I packed boxes for shipment many years ago, distinct markings were required for "combustible", "flammable liquid" and "flammable gas", and they could not be combined within a shipment. I don't know how the handling of the packages differed once I sent them down the conveyor, but at least from a shipping perspective, "combustible" and "flammable" were not the same thing.
    – supercat
    Commented Mar 13, 2014 at 12:49
  • @Jolenealaska: "I almost said (about) the same thing" that's why I upvoted your answer. But I wanted to add the information about combustibility vs. flammability as well and add a technical terminology perspective that I think is important for everyday life. Explosive is still different.
    – cbeleites
    Commented Mar 13, 2014 at 13:20
  • @supercat: flammable substances are always combustible (like highly flammable substances always also meet the definition of flammable). But not every combustible substance is flammable, and not every flammable substance is highly flammable.
    – cbeleites
    Commented Mar 13, 2014 at 13:21
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    In English, hazard symbols and the like have completely abandoned "inflammable". It's as if "inflammable" was never a word. Commented Mar 13, 2014 at 13:37

The prefix "in" typically means to negate the root word. However some word in english have differing origins and therefore do not all follow the same construction rules.

"Inflammable" is one case where the rule above does not apply. Due to the prevalence of the rule being true many less english savvy speakers apply the rule to "inflammable" and think it means "not combustible". Normally a mistake like this would be laughed off but with the dire consequence of getting this one word wrong most safety warning are opting to use "flammable".

So "Unless you are operating such a truck and hence are concerned with the safety of children and illiterates, use inflammable." is stating that if your purpose of writing is to inform of danger use "flammable" because it's less likely to cause injury. For all other reasons use "inflammable" as it is the correct word for educated discourse.

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    Basically, the prefix in-in inflammable is the Latin preposition which means en-, not un- which is used in negation
    – Maulik V
    Commented Mar 13, 2014 at 9:43
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    "Less english savvy speakers" with roman native languages (e.g. French inflammable, Italian infiammabile, Spanish inflamable) of course do not have this difficulty. However, afaik they all share the difficulty that these words are ambiguous with respect to difference between combustible and ease of ignition.
    – cbeleites
    Commented Mar 13, 2014 at 12:02
  • Mind you, it would be awesome if "indubitable" did mean "capable of being put to doubt" just as "inflammable" means "capable of being set on fire" :-) @cbeleites: surely the same ambiguity for "in-" exists in French? "inflammable" vs "incroyable"? I'm not claiming there's misunderstanding what "inflammable" means among French speakers, I don't know. Just that both meanings of "in-" exist and so they could be in doubt, if they wanted. Commented Mar 13, 2014 at 14:58

The final sentence is a sardonic retort, suggesting that if you want to cause someone harm, you may use "inflammable".

A similar example would be:

Feel free to drop your cigarette on the floor, yeah. Even in this forest, at the hottest time of year. If you don't mind setting fire to thousands of square acres and rendering countless hundreds of people homeless, that is...

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    You think so? I read it just the opposite way: For ordinary audiences you should use inflammable. Use flammable only if both the probability and consequences of misunderstanding inflammable are high. Commented Mar 14, 2014 at 23:54
  • @StoneyB: That's certainly your prerogative. On the other hand, I, as a native speaker of English, i.e. being from England, have a full understanding and appreciation of its power of sarcasm and so forth. Commented Mar 15, 2014 at 1:42
  • Oh, I think there's sarcasm there, I just think, from what I know of White (I decline to attach any blame to poor Strunk), that it's directed the other way: "Feel free to trample flat-footedly on My English if you are one of the Infantine and Imbecilic Cretins to whom Linguistic Purity is a Closed Book." Commented Mar 15, 2014 at 1:50

really flammable or inflammable mean the same . first I thought that flammable is the opposite of inflammable but the opposite of flammable or inflammable is non flammable.

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    This simply repeats the existing answers.
    – Chenmunka
    Commented Jan 8, 2015 at 12:36

gasoline trucks used to carry signs stating their contents were flammable and imflammable. This meant that not only were the contents combustible but that they would cause other substances to also combust. The prefix "im-" carried that narrow sense. Analogous usage would be in other words carrying the "im-" prefix, though by no means all with that prefix nor only with it. E.g., "en-gulf" or engulf, uses a version of the Latin "im/n," and there are other instances. Interestingly, however, though one can find evidence of this narrow usage online (usually with bewildered commentary), authoritative references don't include it, not even the OED, which does have a very useful list of other English words with the "im-" prefix describing the outward effect of the word. One can find (using DuckDuckGo, Google and other search engines) instances of writers dismissing "imflammable" as misspelled "inflammable" but I think they miss how it was intended: to signify that not only was the agent, like gasoline, prone to catch fire, but that it could also set other things on fire, too. It would seem that the usage failed to gain popularity or succeeded in being a puzzle. At any rate, it's nigh impossible to find current instances of "imflammable" today; one sees it understood as "inflammable," meaning only that the substance itself is combustible and not that it can also engulf others in flame or, more succinctly, inflame.

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