(something important for situations where people have abilities in more than one variety), and helps in ascertaining where speakers make diaphonic identifications as a result of similarities and differences between the varieties involved. The linguistic variable, a similar concept presented by William Labov, refers to features with variations that are referentially identical but carry social and stylistic meaning. This could include phonological, as well as morphological and syntactic phenomena. Labov also developed variable rules analysis, with variable rules being those that all members of a speech community (presumably) possess but vary in the frequency of use. The latter concept met resistance from scholars for a number of reasons including the argument from critics that knowledge of rule probabilities was too far from speakers' competence. Because of these problems, use of variable rules analysis died down by the end of the 1980s. Nevertheless, the linguistic variable is still used in sociolinguistics. For Labov, grouping variants together was justified by their tendency to fluctuate between each other within the same set of words. For example, Labov presented the variants (among New York speakers) of the vowel of bad or dance: The different phonetic values were assigned numerical values that were then used in an overall score index. Overdifferentiation is when phonemic distinctions from one's primary language are imposed on the sounds of the second system where they are not required; underdifferentiation of phonemes occurs when two sounds of the second system are not maintained because they are not present in the primary system. Dialectology Inspired by , Uriel Weinreich first advocated the use of diasystems in structural dialectology, and suggested that such a system would represent a higher level of abstraction that can unite related dialects into a single description and transcription. While phonemic systems describe the speech of a single variety, diaphonemic systems can reflect the contrasts that aren't made by all varieties being represented. The way these differ can be shown in the name New York. This word may be transcribed phonemically as in American English, as many varieties thereof do not allow the cluster as a syllable onset; in Received Pronunciation, syllable-final doesn't occur so this name would be transcribed to reflect that pronunciation. A diaphonemic transcription such as (with both the and the ) would thus cover both dialects. Neither is described exactly, but both are derivable from the diaphonemic transcription. The desire of building a diasystem to