The declension of Adjectives
1. Adjectives are words which describe nouns. When they come immediately BEFORE the noun, i.e. when they form part of the noun phrase which is the subject or object of the sentence, they must AGREE with the noun in number, gender and case. In other words, they decline. In this position they are called attributive adjectives.
2. When they occur within the predicate of the sentence and NOT immediately before the noun, they are invariable ( 不變的) and DO NOT decline. They are called predicative adjectives.
der junde Mann ( the young man)
der Mann ist jung. (The man is young.)