The meanings of adjectives can be altered by adding a prefix. Most people know that mal- makes opposites, but the meaning of ne- is a bit more vague. How should I know when to use ne- instead of mal-?
Some of them I just know by experience. The only ne-word I can think of right now is nekredebla. Examples with mal- are malsana, malforta and malgaja.
Here are some of the adjectives I am wondering about:
necesa, utila, interesa, grava, certa, klara, kontenta, kapabla, simila, sama