Articulate
Able to speak; able to put one's thoughts into words effectively; uttered in distinct syllables or words.
Inarticulate
Incapable of speech; speechless; unable to express one's thoughts effectively; indistinct
Compatible
Able to get along well together; in agreement
Imcompatible
Unable to get along well together; not in agreement
Fallible
Capable of making a mistake; liable to be inaccurate or false
Infallible
Incapable of being wrong; absolutely reliable; certain; sure
Literate
Able to read and write; educated
Illiterate
Not knowing how to read and write; uneducated
Rational
Able to think and reason clearly; reasonable; sensible
Irrational
Unable to think and reason clearly; contrary to reason; unreasonable; absurd