The aim of this study, which assumes that language is a social phenomenon as well as being a set of rules, is to reconstruct the ontological distinction between necessity and obligation as deontic modality categories. The other aims are to reveal that these categories are individual and social, which have sociolinguistic characteristics and, to present the idea that the obligation should be divided into two as weak and strong obligation in proportion to the power of sanction. In line with these purposes, in this study, both the linguistics literature - which provides the conceptual background on necessity and obligation- and the diachronic-synchronic Turkish literature are discussed. Accompanied by literature review and corpus-based inquiries, strong obligation is marked in the context framed by bureaucratic (written rules and laws), which has not been included in the literature before and in the context determined by the unwritten rules of moral, religious, and social life, it was concluded that weak obligation was marked. Although they are categorically different from each other, bound and free morphemes that mark necessity and obligation in Turkish all belong to the common usage set, thus creating ambiguity. Even lexical items that mark direct necessity or obligation in terms of lexical meaning can be used in different functions, contextually and discursively. For this reason, it would be a more linguistically correct approach to determine the modality values of the sentences at the discursive level, instead of assigning modality values to the categories in question, invariant markers, or only at the morphologic/syntactic level.
Necessity, obligation, sociolinguistics, modality.