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":