Paradigms and morphosyntax
A paradigm is the complete set of related word-forms associated with a given lexeme. The familiar examples of paradigms are the conjugations of verbs, and the declensions of nouns. Accordingly, the word-forms of a lexeme may be arranged conveniently into tables, by classifying them according to shared inflectional categories such as tense, aspect, mood, number, gender or case. For example, the personal pronouns in English can be organized into tables, using the categories of person, number, gender and case.
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. For example, 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. In other words, 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 to be used. In contrast, however, no syntactic rule of English cares about the difference between dog and dog-catcher, or dependent and independent. The first two are just nouns, and the second two just adjectives, and they generally behave like any other noun or adjective behaves.
An important difference between inflection and word-formation is that inflected word-forms of lexemes are organized into paradigms, which are defined by the requirements of syntactic rules, whereas the rules of word-formation are not restricted by any corresponding requirements of syntax. Inflection is therefore said to be relevant to syntax, and word-formation not so. The part of morphology that covers the relationship between syntax and morphology is called morphosyntax, and it concerns itself with inflection and paradigms, but not with word-formation or compounding.