Why doesn't inflammable mean "not" flammable? (in-justice, in-secure, in-complete) Why not just "flammable?"

Answer 1

Mainly because of the verb inflame ( To become excited or aroused, To be affected by inflammation,To catch fire.) somehow developed the added definition of catching fire.

Therefore, inflammable and flammable mean the same thing although the prefix "in" usually indicates antonyms.

Dictionary.com's sagely advice:

Historically, flammable and inflammable mean the same thing. However, the presence of the prefix in- has misled many people into assuming that inflammable means “not flammable” or “noncombustible.” The prefix -in in inflammable is not, however, the Latin negative prefix -in, which is related to the English -un and appears in such words as indecent and inglorious. Rather, this -in is an intensive prefix derived from the Latin preposition in. This prefix also appears in the word enflame. But many people are not aware of this derivation, and for clarity's sake it is advisable to use only flammable to give warnings.

Answer 2

Just one of the many apparent inconsistencies in the English language. I say apparent, because in this case, the terms in question actually come from two different roots...flammable from flame and inflammable from inflame. So in one case, the "ability to catch on fire" comes from the noun meaning the thing which results when it does so, i.e. flame(s), and in the other case, the term comes from verb meaning it has been made to do so, i.e. inflame(d). The word meaning can't be caught on fire is "non-flammable", I have never seen or heard "non-inflammable".

Answer 3

The words inflammable and flammable both mean ‘easily set on fire’, however there are etymology difference between each word:
Inflammable Etymology: French, from Medieval Latin inflammabilis, from Latin inflammare
Flammable Etymology: Latin flammare to flame, set on fire, from flamma

Both words can be use as:
• adjective, meaning easily set on fire.
• noun, meaning a substance which is easily set on fire.

It is, however, safer to use flammable if one wishes to avoid ambiguity, as the in- prefix of inflammable can give the impression that the word means ‘non-flammable’.

So at the end, the reasion is the etymology of each word

Answer 4

Your first respondent has a pretty good answer for you. I would only correct that "inflame" did not somehow eventually come to mean "to ignite into flame". That was always its meaning. The application of the term to physical conditions (i.e., inflammation) was part metaphorical, part consequence of the primitive medical knowledge they had.

Often, the verbs that began with an "in" in Latin or Middle French would change to start with "en" once in English (e.g., encumber, envelop, enhance). This one didn't change.