Morphological derivation, in linguistics, is the process of forming a new word from an existing word, often by adding a prefix or suffix, such as un- or -ness. For example, unhappy and happiness derive from the root word happy. It is differentiated from inflection, which is the modification of a word to form different without changing its core meaning: determines, determining, and determined are from the root determine. Derivational morphology often involves the addition of a derivational suffix or other affix. Such an affix usually applies to words of one (part of speech) and changes them into words of another such category. For example, one effect of the English derivational suffix -ly is to change an adjective into an adverb (slow → slowly). Here are examples of English derivational patterns and their suffixes: adjective-to-noun: -ness (slow → slowness) adjective-to-verb: -en (weak → weaken) adjective-to-adjective: -ish (red → reddish) adjective-to-adverb: -ly (personal → personally) noun-to-adjective: -al (recreation → recreational) noun-to-verb: -fy (glory → glorify) verb-to-adjective: -able (drink → drinkable) verb-to-noun (abstract): -ance (deliver → deliverance) verb-to-noun (agent): -er (write → writer) However, derivational affixes do not necessarily alter the lexical category; they may change merely the meaning of the base and leave the category unchanged. A prefix (write → re-write; lord → over-lord) rarely changes the 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- (replaced by em- before labials) is usually a transitive marker on verbs, but it 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).