The Allen and Greenough is still under construction;
so some links may not work quite the way you would expect.
109. Adjectives and Participles are in general
formed and declined like Nouns, differing from them only in their use.
1. In accordance with their use, they distinguish gender by different
forms in the same word, and agree with their nouns in gender,
number, and case. Thus, -
- bonus puer, the good
- bona puella, the good
- bonum dónum, the
2. In their inflection they are either (1) of the First and Second
Declensions, or (2) of the Third Declension.