Long form Short form Wrong usage
опасный преступник (a dangerous criminal) он опасен! (he is dangerous!) он опасный!(sounds awkward)
согласный (someone who agrees) он согласен он согласный(wrong)

 

Short adjectives are modified by the gender and number only, not by case(some exceptions that remained from old russian: на босу ногу, средь бела дня). Masculine short adjectives in the sinsular form have zero ending, whereas feminine adjectives in the singular form have -a ending, and singular neuter adjectives in the singular form -o ending. Short adjectives in the plural have ending.

 

Singular Plural
Masculine (zero ending) Neuter () Feminine()
согласен (someone who agrees) согласно согласна согласны
приятен (pleasant, nice) приятно приятна приятны
достоен (deserving,worthy) достойно достойна достойны


Short forms for the adjectives большой and маленький are велик and мал

Some adjectives that do not have a short form are:

  1. most color names: оливковый, синий (olive,blue)
  2. subjective atiitude adjectives: хорошенький, злющий (something good & little, very very angry)
  3. some other types: боевая награда (military award), ближний путь(closest way) etc

Some on the contrary do not have a full form: великоват (too large), маловат (too small), рад (glad) and others.