"in" v. "un"

No. Inflammable mean the same as flammable - not at all the same as unflammable.

Looks like it depends on the etymology of the word to be modified. Old English or German based words use un-; Middle English or French/Latin words us in-.

Main Entry: 1in-
Variant(s): or il- or im- or ir-
Function: prefix
Etymology: Middle English, from Middle French, from Latin; akin to Old English un-
: not : NON-, UN- -- usually il- before l <illogical>, im- before b, m, or p <imbalance> <immoral> <impractical>, ir- before r <irreducible>, and in- before other sounds <inconclusive>


Main Entry: 1un-
Pronunciation: "&n, often '&n before '-stressed syllable
Function: prefix
Etymology: Middle English, from Old English; akin to Old High German un- un-, Latin in-, Greek a-, an-, Old English ne not -- more at NO
1 : not : IN-, NON- -- in adjectives formed from adjectives <unambitious> <unskilled> or participles <undressed>, in nouns formed from nouns <unavailability>, and rarely in verbs formed from verbs <unbe> -- sometimes in words that have a meaning that merely negates that of the base word and are thereby distinguished from words that prefix in- or a variant of it (as im-) to the same base word and have a meaning positively opposite to that of the base word <unartistic> <unmoral>
2 : opposite of : contrary to -- in adjectives formed from adjectives <unconstitutional> <ungraceful> <unmannered> or participles <unbelieving> and in nouns formed from nouns <unrest>

Nice Drew Dad - thanks!

Now, knowing this, what do we make of Roger's excellent example?

Maybe it's a "rule" like that whole "i before e" malarky.

There was a second definition for in- that I did not include.

I suspect that "inflammable" comes from "inflame."