In some models of phonology as well as morphophonology in the field of linguistics, the underlying representation (UR) or underlying form (UF) of a word or morpheme is the abstract form that a word or morpheme is postulated to have before any phonological rules have been applied to it.[1][2] In contrast, a surface representation is the phonetic representation of the word or sound. The concept of an underlying representation is central to generative grammar.[3]
If more phonological rules apply to the same underlying form, they can apply wholly independently of each other or in a feeding or counterbleeding order. The underlying representation of a morpheme is considered to be invariable across related forms (except in cases of suppletion), despite alternations among various allophones on the surface.