The article deals with the context-discursive development factors of the modal meanings of the Middle English verb “may / mighte”. The context reinterpretation of its dynamic meanings is taken as a starting point of the manifestation of the deontic and epistemic senses. The research conducted by the material of G. Chaucer’s “The Canterbury Tales” shows that one of the key pragmatic factors of the semantic development of “may / mighte” is the context subjectification.