Surface filter

rdf:langString Surface filter

rdf:langString In linguistics, a surface filter is a type of sound change that operates not at a particular point in time but over a longer period. Surface filters normally affect any phonetic combination that is not permitted according to the language's phonetic rules and so preserve the phonotactics of that language. They are also often a source of complementary distribution between certain sets of sounds. A trivial example of a surface filter is the replacement of sounds foreign to a language with sounds native to the language. For example, a language that has no front rounded vowels may replace such vowels with either front unrounded or back rounded vowels, whenever it borrows a word containing such a vowel. Strictly speaking, that is not a surface filter, as it is merely the way in which the phonetics of one language are matched to that of another. That example, however, still illustrates the importance of surface filters in preserving the phonological structure of words within the language. Usually, the term applies only to rules that affect both native and borrowed words.