Inflection defines congruence relations and government relations between words and their immediate syntactic context, in terms of Case, Number, Gender, Person, Tense, and, on the basis of the semantic interpretation of these relations, deictic relations and role relations between words and their context of utterance.
Congruence relations determine that the forms of two parts of speech in the same syntactic context are interdependent (e.g. Number with nouns and articles, or with nouns and verbs).
Government relations determine that the forms of one part of speech depend on valency or subcategorisation properties of another (e.g. intransitive or transitive verbs).