The data of the present article was collected through a randomly classified data collection process, a questionnaire, and a speech completion test; the data, then, was analyzed through the statistical square method. The hypothesis of the present research is that Tehrani dialect is different from other Persian dialects (Isfahani, Shirazi, Mashadi, and Lori dialect) regarding its vocalic Conformity. The conclusion of the research is that in addition to intra-linguistic and linguistics-related factors, the following extra-linguistic factors also affect the use of vocalic Conformity: the frequency of occurrence of the linguistic element, prestige, exposure to mass media, formality or informality of the context, and whether the intended dialect is learnt as the second language or not. The final conclusion is that linguistic and linguistics-related realities should be taken as effects rather than factors.