Why do "flammable" and "inflammable" mean the same thing?

This was probably covered already, but I haven’t seen it. It’s just one of those English language things that have bugged me lately.

“inflammable” comes from the word “inflame”: capable of being inflamed.

However, some people believe that “in” can only mean “not” (e.g., inedible, incredible). So they would pick up a can of gasoline, see the word “inflammable” and figure it was all right to use it to put out a fire.

To prevent this sort of messy evolutionary advance, safety officials pushed for the use of the word “flammable.”


They mean the same thing, but not the exact same thing.

Flammable is from the latin flammare: to burn.

inflammable is a combination of the words “in” and “flame”

So, flammable implies that the object itself can flame. Inflammable implies that the object can be consumed in flames.

It’s hard to imagine the difference, because in the physical world, there probably is no difference. Maybe there is. But there surely is a difference theoretically.

Just a side note that’s not completely tangent:

When we want to describe a person who is easily provoked, we say he is inflammable, NOT that he is flammable.

This sorta illustrates the difference: the person isn’t angry intrinsically; he just has the tendency to become consumed in anger at the moment.

The Ministry of Newspeak has determined your theoretical actual submission would be better served at the Bureau of Doubletalk.

{{{This was probably covered already, but I haven’t seen it.}}}—JumP Zero

George Carlin is generally considered The Guru on the subject.

(The Original EnigmaOne)
Common ¢ for all ages.

I was under the impression (possibly mistaken, but nonetheless…) that the prefix “in-” can be used as an intensifier…that is, its use emphasizes even more the characteristic it modifies. Inflammable objects are more flammable than merely flammable ones. Compare to invaluable. Something that is invaluable is extermely valuable.

But perhaps “in-” prefix in this case still means “not”. Something that is invaluable may also be looked at as being so desired–so precious–that one could not possible put a value on it–it is not capable of being valued. But this may be stretching it.
Chemically, one compares flammability of various liquids by measures such as the “flashpoint” temperature. This is the temperature a substance will erupt into flames in normal atmosphere in the presence of an ignition source. (I’m not an expert–there are exacting ways these measurements can and are done, and there are other kinds of tests, too) Some liquids are extremely flammable, for example acetone or ether, with flashpoints <100C (guessing). One might classify these as inflammable to differentiate them from liquids with higher flashpoint temperatures such as gasoline.

According to Mirriam-Webster, ‘inflammable’ was first used in 1605, and ‘flammable’ in 1813. Likely, ‘flammable’ was created for much the reason postulated by Reality Chuck, though obviously in 1813 it wasn’t gasoline fuel that caused the creation of the word.

I would recommend reference to the O.E.D. if anyone wants to delve more thouroughly into the etymology involved.