It is often reasonable to assume that the isolation form of a morpheme provides its underlying representation. For example, in some varieties of American English, "plant" is pronounced , while "planting" is , where the morpheme "plant-" appears in the form . Here, the underlying form can be assumed to be , corresponding to the isolation form, since rules can be set up to derive the reduced form from this (but it would be difficult or impossible to set up rules that would derive the isolation form from an underlying ).