Derivational vs. Inflectional Morphology

The two basic categories of morphology are derivational morphology and inflectional morphology, and the distinction frames the entire field. It rests on a prior contrast between two kinds of morphemes: functional morphemes and lexical morphemes.

Functional and lexical morphemes

A functional morpheme is a meaningful grammatical element that usually has a logical meaning. In the example sentence the dermatologist hugged a pretty girl who was well read in the latest journal articles on the breeding of oxen, the functional morphemes include the, a, who, in, on, and of, as well as the -ed suffix on hugged. A lexical morpheme, by contrast, is a meaningful lexical element that usually has an abstract meaning, with at least some elements that cannot be represented purely logically; examples include dermatologist, hug, pretty, and girl.

Several properties track this split. Functional morphemes normally have logical meanings, whereas lexical morphemes lack a purely logical meaning, though this does not mean lexical morphemes contain no logical components at all. The inventory of functional morphemes is a closed class: it is limited, and creating a new functional morpheme is very hard, though it does happen. Lexical morphemes form an open, unlimited class, with new words added all the time. Typical functional categories include gender, number, determiner, tense, aspect, degree words, wh-elements, and negation; typical lexical categories are verbs, nouns, adjectives, and adverbs.

Two kinds of morphology

This split maps directly onto the two branches of morphology. Derivational morphology is all about the creation of lexical morphemes, while inflectional morphology is all about the marking of grammatical elements on words by means of functional morphemes.

The two branches answer different questions. Derivational morphology helps determine what a lexical morpheme is and what it means, dealing with lexical items and how words are formed. Inflectional morphology helps determine what a particular noun, verb, or adjective means in context, along with its grammatical role in the sentence, dealing with grammatical items that carry logical meanings. Studying derivation therefore means studying how words come into being; studying inflection means studying how those words are grammatically marked and interpreted once formed.