[help]Can you tell me something about these word ?

possible... impossible

balance... imbalance

tie... untie

screw... unscrew

i don't know of any word that becomes it's opposite by adding "in-".

I'm sure Jim will be able to give a better explanation, and there are probably a lot of exceptions, but if the original word starts with a p, m, b or any other sound that has your lips together, you use the IM-.

I'm not sure about IN- vs. UN- though. I'm trying to think of other words that start with a vowel to find one that uses UN, but a lot of the vowels do seem to use IN-.

ability/inability; effective/ineffective; opportune/inopportune

possible... impossible

balance... imbalance

tie... untie

screw... unscrew

i don't know of any word that becomes it's opposite by adding "in-".

p.s. (after getting proper sleep)

appropriate... inappropriate

visible... invisible

my apologies for the lack of words a while ago. i was incomplete, half-asleep, semi-zombie. the words becoming opposite with "in-" came to me in my sleep. i woke up right after i thought of these - as if i had a nightmare. HAHA