For many years scholars have endeavoured to define what a language is and address how it is different from other types of language varieties such as dialect and accent. Some studies identify language varieties based on their structural similarity, focusing on the lexical similarity, and the phonological, morphological and syntactic properties. Others adopt a functional approach and focus on the degree to which speakers of language varieties "…can understand each other based on knowledge of their own language variety without needing to learn the other language variety, at a functional level" (Eberhard et al., 2021, p.1). Some studies address language identification issues following an ethnographic approach. These studies investigate language as a communicative behavior used by members of a particular culture (Hymes, 1989). Finally, studies which adopt a folk linguistic approach to language underline the linguistic perspectives of folk (non-specialists). Available studies in the field of Iranian linguistics adopt a predominantly structural approach to identify different types of language varieties. Given this imbalance in the literature, this dissertation chronicles the development of a measurement tool in the context of an exploratory mixed methods research project. Based on available literature, initial qualitative study results and an expert panel's views, I developed a sociolinguistic questionnaire. Following rigorous steps in questionnaire validation (Hinkin, 1998), I validated this questionnaire with 5 components and 21 statements. To treat folk perspectives as meaningful in their own right alongside the perspectives of scholars, this questionnaire investigated the linguistic perspectives of participants from a cross-section of speech communities in Iran. The questionnaire further identified the parameters associated with these perspectives in defining and differentiating different types of language varieties. Results indicated that parameters including language variety status, extent of mutual intelligibility and shared words between language varieties, and standardized writing systems were the parameters which statistically significantly influenced Iranian folk perspectives. Perspectives regarding the relevance of urban vs. rural geography and number of speakers were heterogeneous. Results further showed that in language identification, the participants' education, prior formal knowledge of linguistics, and mother tongue predicted 53% of the variation in their linguistic perspectives among the sample population.