A dialect continuum or dialect area was defined by Leonard Bloomfield as a range of dialects spoken across some geographical area that differ only slightly between neighboring areas, but as one travels in any direction, these differences accumulate in such a way that speakers from opposite ends of the continuum are no longer mutually intelligible. (This is analogous to a ring species in evolutionary biology.) The lines that can be drawn between areas that differ with respect to any feature of language are called isoglosses. According to the abstand and ausbau languages paradigm, these dialects can be considered abstand languages (i.e., as stand-alone languages by linguistic distance). However, they can be seen as dialects of a single language, provided that a common standard language exists through which communication is possible (a Dachsprache).