inflection, in grammar. In many languages, words or parts of words are arranged in formally similar sets consisting of a root, or base, and various affixes. Thus walking, walks, walker have in common the root walk and the affixes -ing, -s, and -er. An inflectional affix carries certain grammatical restrictions with it; for example, with the plural inflection -s, a change from singular to plural in the noun tree/trees requires a concommitant change in the verb form from singular to plural: "the tree is green," "the trees are green." Other examples of English inflectional suffixes are the verb tenses. Many languages have far more extensive inflection than English, e.g., Latin, Eskimo, Arabic. In Latin grammar the typical noun and adjective are inflected for case and number, and the adjective is additionally inflected for the gender of the noun. Latin verbs have overlapping categories of inflection: mood, voice, tense, person, and number. Noun inflection is called declension, and the inflection of verbs is called conjugation. To be distinguished from inflectional affixes are those of derivation. Derivation is the process of forming words from other words or roots by the addition of affixes that in themselves either have meaning or denote word function. Derivational affixes in English may be either prefixes—e.g., de-press, un-common—or suffixes—e.g., work-er, retire-ment, happi-ness. The name stem is given to a root together with its derivational affixes; thus in racket-eer-s, racket is the root, racketeer the stem, and -s the plural inflection. Beginning in the 19th cent., the modification of a root or base by the amount of inflection or derivation in a language was used as a basis for classification. An isolating language is one in which there are only roots, with no derivation or inflection, such as Chinese. On the other hand, inflected languages, e.g., English and Latin, use roots, stems, and affixes, but the amount of inflection is not as great as in agglutinative languages where roots and affixes are readily identifiable, e.g., Turkish baba "father," babam "my father," babama "to my father." The old belief that agglutinative languages were the most primitive and isolating languages the most civilized is no longer held, it being recognized that every language is just as expressive as any other and can develop new vocabulary to fit new situations. See ablaut; grammar; umlaut; English language.