A short article this time, on the topic of adjectives and prefixes. Many languages have prefixes that turn adjectives into their opposites. The most common one in English is the prefix un (unhappy, unlucky, unusual etc.) Unfortunately for the learner, however, there are several other prefixes of this type, including in- (incorrect), dis- (dishonest), il- (illegible), ir- (irregular), and im- (impolite), and so the opposite form cannot be predicted with any certainty.
The learner is also faced with certain rogue adjectives that don't behave as they should. Having established that unlucky is the opposite of lucky, for example, the learner may be surprised to find out that uneasy is not the opposite of easy; and that the word appointed* is not an adjective and not the opposite of disappointed. Similarly, he will be a little puzzled to learn that invaluable is not the opposite of valuable and does not mean having no value or worthless. And take that famous pair: flammable and inflammable. Who could guess that they mean exactly the same, i.e. describing a material that burns easily. In fact, the word for something that does not burn (easily) is non-flammable.
(* Appointed is not used alone as an adjective, but can be used together with an adverb like well or excellently to describe the furnishings in a room. E.g. My sister has a large house with well-appointed rooms.)
No doubt the learner will relinquish any expectation of consistency in English on discovering that although the opposite of the adjective able is unable, the opposite of its noun form is inability.
Look at these adjectives beginning with in- and decide if there is a form without the prefix. If there is, say whether that word is the genuine opposite of the in- word. If it isn't, say what the other word means.