Two forms with opposite meanings are called antonyms. Some common examples are the pairs: alive/dead, big/small, fast/slow, happy/sad, hot/cold, long/short, male/ female, married/single, old/new, rich/poor, true/false.

Antonyms are usually divided into two main types, “gradable” (opposites along a scale) and “non-gradable” (direct opposites). Gradable antonyms, such as the pair big/ small, can be used in comparative constructions like I’m bigger than you and A pony is smaller than a horse. Also, the negative of one member of a gradable pair does not necessarily imply the other. For example, the sentence My car isn’t old, doesn’t necessarily mean My car is new.

With non-gradable antonyms (also called “complementary pairs”), comparative constructions are not normally used. We don’t typically describe someone as deader or more dead than another. Also, the negative of one member of a non-gradable pair does imply the other member. That is, My grandparents aren’t alive does indeed mean My grandparents are dead. Other non-gradable antonyms in the earlier list are the pairs: male/female, married/single and true/false.

Although we can use the “negative test” to identify non-gradable antonyms in a language, we usually avoid describing one member of an antonymous pair as the negative of the other. For example, while undress can be treated as the opposite of dress, it doesn’t mean “not dress.” It actually means “do the reverse of dress.” Antonyms of this type are called reversives. Other common examples are enter/exit, pack/unpack, lengthen/shorten, raise/lower, tie/untie.