 These cases, where the same distinction is effected by alternative forms of a "word", constitute allomorphy.Phonological rules constrain which sounds can appear next to each other in a language, and morphological rules, when applied blindly, would often violate phonological rules, by resulting in sound sequences that are prohibited in the language in question.For example, to form the plural of "dish" by simply appending an "-s" to the end of the word would result in the form , which is not permitted by the phonotactics of English.