Adjective theory in German grammar focuses on understanding the role and usage of adjectives within sentences. Adjectives in German play a crucial role in describing and modifying nouns. They agree with the gender, number, and case of the noun they are associated with.

One key aspect of adjective theory is the concept of strong and weak inflection. Adjectives in their basic form have a weak inflection when they are preceded by definite articles or other determiners, showing agreement with gender and case. On the other hand, strong inflection is used when there are no definite articles or determiners preceding the adjective, and the adjective must indicate gender, number, and case.

Practical applications of adjective theory include understanding the declension of adjectives depending on the case of the noun they modify, as well as the formation of comparative and superlative forms. Furthermore, it is important to know the specific rules for adjective endings based on the gender, number, and case of the noun.

Overall, a solid understanding of adjective theory in German grammar is essential for constructing grammatically correct and coherent sentences.