A affix is a morpheme attached to a base or root inside a word that alters its meaning or grammatical function. Affixation is a central mechanism in grammar, used to express tense, number, case, negation, derivation and other linguistic categories, and it can affect how a term behaves in a sentence.

Common positions

  • Prefix — added to the beginning of a root (English un- in unhappy).
  • Suffix — attached to the end of a root (English -s in cats).
  • Infix — inserted inside a root (rare in English, more common in other languages; English expletive insertion is an informal example).
  • Circumfix — made of two parts that surround a root (found in languages such as German for some verb forms).
  • Interfix — a linking element used in compound formation (a connective vowel appearing between stems in some languages).

Functions: inflection vs derivation

Affixes serve two broad roles. Inflectional affixes modify a word’s grammatical features without changing its core lexical category (for example, marking plural, tense or case). Derivational affixes create new words or change the part of speech (for example, forming a noun from a verb or creating opposites). The distinction is important because derivational processes often change meaning and category, while inflectional processes typically preserve the base meaning and add grammatical information.

Properties and behaviour

  • Affixes are generally bound morphemes, meaning they cannot stand alone and must attach to another element.
  • Many affixes exhibit allomorphy — a single affix may have different surface forms depending on the sound environment (English plural spelled -s but pronounced in several ways).
  • Ordering matters: multiple affixes on one stem often appear in a language-specific sequence; swapping them can change meaning or produce an ungrammatical form.
  • Clitics are related but distinct: they attach to words like affixes but retain some syntactic independence.

Cross-linguistic notes

The role and richness of affixation vary widely. Agglutinative languages (e.g., Turkish) tend to stack many separate affixes that each mark a single grammatical category, while fusional languages (e.g., Spanish) often use affixes that encode several grammatical features simultaneously. Some languages rely more on word order or particles instead of affixation to express grammatical relationships.

Examples

  • Prefixes: re- (again) in replay, dis- (negation) in disagree.
  • Suffixes: -ed (past tense) in walked, -er (agent) in writer.
  • Circumfix: German past participles formed with ge- ... -t in many regular verbs.

Affixation is one of the primary ways languages build new forms and encode grammatical information; studying affixes helps explain patterns of word formation and sentence structure in the grammar of any language.