 The inflectional categories used to group word forms into paradigms cannot be chosen arbitrarily; they must be categories that are relevant to stating the syntactic rules of the language.Person and number are categories that can be used to define paradigms in English, because English has grammatical agreement rules that require the verb in a sentence to appear in an inflectional form that matches the person and number of the subject.Therefore, the syntactic rules of English care about the difference between "dog" and "dogs", because the choice between these two forms determines which form of the verb is used.