No, No, No!
Greetings,
As we hurl ourselves at the third (or fourth, depending on your mathematical persuasion) year of the new millennium, and everyone is being all positive and gung-ho, making and breaking New Year's resolutions with gay abandon, I thought this would be a good time to focus on the negative ... because negatives are easier to understand ... or are they?
As Lavinia said, stamping her daintily-clad foot just the other day, "No, no, a thousand times no!"
In English, we often form negatives by adding a prefix to words:
likely - unlikely
understood - misunderstood
complete - incomplete
modest - immodest
reversible - irreversible
logical - illogical
Not really all that logical, is it? All those different prefixes, all meaning the same thing ... NO!
But you can be pretty sure that if you add a prefix to a word, you're changing its meaning ... Umm ... except for words like "flammable" and "inflammable."
If something is "flammable" it means it will burn readily ... right? So ... if it's "inflammable" that should mean it doesn't burn ... right?
Wrong. Both words mean the same.
Visitors to the Apostrophe Forum have been addressing this problem of flammable and inflammable materials. Richard Tinsley did some investigating and found the following satisfactory explanation at the Word Detective site: http://www.word-detective.com/120398.html
Blame it on Latin and its tricky prefixes. In the beginning, there was "inflammable," a perfectly nice English word based on the Latin "inflammare," meaning "to kindle," from "in" (in) plus "flamma" (flame). "Inflammable" became standard English in the 16th century. So far, so good.
Comes the 19th century, and some well-meaning soul dreamt up the word "flammable," basing it on a slightly different Latin word, "flammare," meaning "to set on fire." There was nothing terribly wrong with "flammable," but it never really caught on. After all, we already had "inflammable," so "flammable" pretty much died out in the 1800's.
"But wait," you say, "I saw 'flammable' just the other day." Indeed you did. "Flammable" came back, one of the few successful instances of social engineering of language.
The Latin prefix "in," while it sometimes means just "in" (as in "inflammable"), more often turns up in English words meaning "not" (as in "invisible" -- "not visible"). After World War Two, safety officials on both sides of the Atlantic decided that folks were too likely to see "inflammable" and decide that the word meant "fireproof," so various agencies set about encouraging the revival of "flammable" as a substitute. The campaign seems to have worked, and "inflammable" has all but disappeared.
That left what to call something that was not likely to burst into flames, but here the process of linguistic renovation was easier. "Non-flammable" is a nice, comforting word, and besides, it's far easier on the tongue than its now thankfully obsolete precursor, "non-inflammable."
The Oxford English Dictionary adds this usage note: 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.
Hope this helps. =)
Article from : http://www.write101.com/W.Tips215.htm