Examples
One very common example of a surface filter isApplication
Surface filters are often formed as a result of sound changes that change the phonetic makeup, and certain sounds or combinations no longer occur in the language. As a consequence, speakers no longer learn to pronounce such combinations and so have difficulty with new words that violate the principles. Then, either the phonology of the language is extended to incorporate such new combinations, or the "inconvenient" combinations are automatically reconstructed into a form that conforms to the phonotactics of the language. If the reconstruction occurs systematically and becomes part of the phonology of the language, the result is a surface filter. Such phonological rules may continue to apply for an indefinite amount of time. Final-obstruent devoicing in Dutch, for example, has been a phonological rule since