Why do flammable and inflammable mean the same thing?
Bert Friedman asks why flammable and inflammable mean the same thing. He also asked why Superman could stop bullets with his chest, but always ducked when someone threw a gun at him. Bert, Bert, we love you for yourself, not your insouciant wit!
Certainly his first question is worthy of review. After all, insouciant means carefree (i.e., not caring), infidelitous means not faithful, informal means not formal, and so on. So why doesn’t inflammable mean not easily set on fire?
The answer lies in the etymology of the word. You see, there are two Latin prefixes, both spelled in, and they have quite different effects on the words to which they are attached. All the above examples derive from the in which is synonomous with the Greek a and the Germanic un, meaning not, without or lacking.
Inflammable is derived from the in meaning in, on, into, towards or within. In French, this prefix evolved into en, and inflammable comes from the Old French word enflammer, which further derives from this second Latin prefix in plus flamma, meaning flame.
Flammable is a later invention, created exactly because inflammable can easily be mistaken for a negative. The true opposite of inflammable is non-flammable.
Oh, and Superman dodges guns because of his concern that weapons ricocheting off his chest might discharge in unpredictable directions, endangering civilians. Hope that clears things up, Bert!