Many languages use the morphological processes of inflection to modify or elaborate on the meaning of words. In some languages words are built of several meaningful units called morphemes, the English word "unexpected" can be analyzed as being composed of the three morphemes "un-", "expect" and "-ed". Morphemes can be classified according to whether they are roots to which other bound morphemes called affixes are added, and bound morphemes can be classified according to their position in relation to the root: prefixes precede the root, suffixes follow the root and infixes are inserted in the middle of a root. Affixes serve to modify or elaborate the meaning of the root. Some languages change the meaning of words by changing the phonological structure of a word, for example the English word "run" which in the past tense is "ran". Furthermore morphology distinguishes between processes of inflection which modifies or elaborates on a word, and derivation which instead creates a new word from an existing one - for example in English "sing" which can become "singer" by adding the derivational morpheme -er which derives an agentive noun from a verb. Languages differ widely in how much they rely on morphology - some languages, traditionally called polysynthetic languages, make extensive use of morphology, so that they express the equivalent of an entire English sentence in a single word. For example the Greenlandic word "oqaatiginerluppaa" "(he/she) speaks badly about him/her" which consists of the root oqaa and six suffixes.[18]