Why do flammable and inflammable mean the same thing?

Answer 1

inflammable is an old word according to dictionary.com it's about 200 yrs old-Flammable is used as a technical term meaning combustible as in gas and inflammable is use more as non technical as in his speech ignited inflammable emotions of the crowd.

Answer 2

The prefix “in-” does not indicate negation here; it comes from the word "inflame.” “Flammable” and “inflammable” both mean “easy to catch on fire”; but so many people misunderstand the latter term that it’s better to stick with “flammable” in safety warnings.


Flammability or Inflammability is the ease with which a substance will ignite, causing fire or combustion. Materials that will ignite at temperatures commonly encountered are considered flammable, with various specific definitions giving a temperature requirement.


Flammable. 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 explosives are now marked FLAMMABLE. Unless you are operating such a truck and hence are concerned with the safety of children and illiterates, use inflammable

This is one of those word errors in the English language.

Answer 3

"Should you be careful with a solvent that’s inflammable? Absolutely. The trouble with flammable and inflammable is that they mean the same thing. The prefix in- is not the Latin negative prefix in-, which is related to the English un- and appears in such words as indecent and inglorious. The in- in inflammable is an intensive prefix that is derived from the Latin preposition in. This prefix also appears in the word enflame. But many people are ignorant of all this and conclude that, since flammable means 'combustible,' inflammable must mean 'not flammable' or 'incombustible.' Therefore, for clarity’s sake, you should use only flammable to give warnings."

Answer 4

Flammable is of relatively recent origin. However, it has in many contexts (especially safety) taken the place of the older Inflammable, which many people take to mean its exact opposite (assuming that the Latin prefix in- always means "not", when in this case it is an intensifer). Because of this confusion, the word "inflammable" (on its own) is avoided in technical usage (warning notices, etc). In, for example, the United States and the United Kingdom, trucks carrying gasoline and other (in)flammable substances are always marked "flammable". In other countries, such as India, the words "highly inflammable" are used.

Answer 5

Because inflammable is derived from the word inflame, which means to set alight. Flammable means it is very easily inflamed!

Answer 6

Contrary to the interpretation that in- has a negative meaning, here it means "in" (inflammable - able to be on fire, flammable - able to catch a fire/flames)
http://dictionary.reference.com/browse/inflammable

Answer 7

Because English is a horrible language :)

The reality is that our language is always changing because of the influx of so-called "foreign" words. Different people bring different words, and to communicate effectively, we learn to use them both.

That's the reason we can pare a pair of pear, and how "raze" (pronounced the same was as "raise") means to tear down instead of build up. If someone asks you verbally to "raise" a building, you better clarify the spelling!

Answer 8

For the same reason that 'passive' and 'impassive' mean the same thing, I guess.

Answer 9

Just a quirk of American language, I guess. There are a few others like that.

Answer 10

word evolution