In linguistics, derivation is the process of forming a new word on the basis of an existing word, e.g. happiness and unhappy from happy, or determination from determine. It often involves the addition of a morpheme in the form of an affix, such as -ness, un- and -ation in the preceding examples.
Derivational morphology often involves the addition of a derivational suffix or other affix. Such an affix usually applies to words of one lexical category (part of speech) and changes them into words of another such category. For example, the English derivational suffix -ly changes adjectives into adverbs (slow → slowly).
Examples of English derivational patterns and their suffixes:
However, derivational affixes do not necessarily alter the lexical category; they may merely change the meaning of the base, while leaving the category unchanged. A prefix (write → re-write; lord → over-lord) will rarely change lexical category in English. The prefix un- applies to adjectives (healthy → unhealthy) and some verbs (do → undo), but rarely to nouns. A few exceptions are the derivational prefixes en- and be-. En- (em- before labials) is usually used as a transitive marker on verbs, but can also be applied to adjectives and nouns to form transitive verbs: circle (verb) → encircle (verb); but rich (adj) → enrich (verb), large (adj) → enlarge (verb), rapture (noun) → enrapture (verb), slave (noun) → enslave (verb).
Derivation can also occur without any change of form, for example telephone (noun) and to telephone. This is known as conversion, or zero derivation.
Derivation that results in a noun may be called nominalization. This may involve the use of an affix (as with happy → happiness, employ → employee), or may occur via conversion (as with the derivation of the noun run from the verb to run).
Generally speaking, inflection applies in more or less regular patterns to all members of a part of speech (for example, nearly every English verb adds -s for the third person singular present tense), while derivation follows less consistent patterns (for example, the nominalizing suffix -ity can be used with the adjectives modern and dense, but not with open or strong). However, it is important to note that derivations and inflections can share homonyms, that being, morphemes that have the same sound, but not the same meaning. For example, when the affix -er, is added to an adjective, as in small-er, it acts as an inflection, but when added to a verb, as in cook-er, it acts as a derivation.
Derivation can be contrasted with other types of word formation such as compounding. For full details see Word formation.
Note that derivational affixes are bound morphemes – they are meaningful units, but can only normally occur when attached to another word. In that respect, derivation differs from compounding by which free morphemes are combined (lawsuit, Latin professor). It also differs from inflection in that inflection does not create new lexemes but new word forms (table → tables; open → opened).
Derivational patterns differ in the degree to which they can be called productive. A productive pattern or affix is one that is commonly used to produce novel forms. For example, the negating prefix un- is more productive in English than the alternative in-; both of them occur in established words (such as unusual and inaccessible), but faced with a new word which does not have an established negation, a native speaker is more likely to create a novel form with un- than with in-.