the contrary

[atadri]

hi,
I'd like to know the prefix which indicates the contrary such as : able unable, unforeseeable................
Regards
atadri

[Philly]

There are a number of negative prefixes. Unfortunately, there aren't any easy rules for when to use which one. Here are the most common ones (each with an example):
.
un- unreasonable
im- impossible
in- inappropriate
ir- irregular
il- illegal
dis- dissatisfied

[Tdol]

Ig- ignoble

[BobK]

a-: asymmetry, amoral
[When the positive word starts with a vowel, this becomes an-: anæsthetic.]
anti-: anticlockwise
counter-: counter-revolutionary
contra-: contradistinction

There are probably more, but as Philly said, hers are the most common.

b