SUMMARY
The aim of the research. The paper is to clarify the role of socio-psycholinguistic factors of lexical units ‘till’/‘until’ functioning in present-day English. The research is focused on the lexical units ‘till’/‘until’, which are the objects of functional transposition, as a result of which both units are determined and function as prepositions and conjunctions, are defined by the identical vocabulary definitions, derive from the same part of speech – preposition and undergo functional transposition into the category of conjunction. Nevertheless, they are characterized by a diverse level of institutionalization in the language, what is proved by the statistical data. Therefore we put forward the hypothesis that the divergences in applying the units depend on the socio-psycholinguistic factors, which characterize the speech at the present stage of the language development and determine the institutionalization level of any transpositional process.Methods. The analysis is represented by the corpus-based and corpus-driven research and is grounded on the data, retrieved from the British National Corpus (BNC) as the most balanced and representative source of written and oral extracts of the English language. Under the research, socio-psycholinguistic factors are divided into linguistic, viz. discourse type, text type, derived text type, text domain, context-governed text domain and type of interaction, the level of difficulty, and socio-psychological factors, viz. age and gender of an author (for written discourse), age, gender, and social class of a speaker and respondent (for spoken discourse).Results and conclusion. The obtained data testify that there are almost no difference between the preposition and conjunction ‘till’, except for the authors’ and speakers’ age. The figures of the categories prove the further expansion of the preposition ‘till’. The preposition and conjunction ‘until’ are characterized by more profound divergences, in particular, on the side of linguistic factors. Taking into account the fact that socio-psychological factors determine the linguistic peculiarities of the language units in discourse, it is worth stating that the preposition ‘until’ is characterized by the lowest number of points of intersection with other units under study, which predetermines its potential for further analysis from the perspective of modern psycholinguistics.