Strictly speaking, Bakhtin's constant and central critical preoccupation is with a (diachronically biased) poetics of the novel. However, for Bakhtin there is no 'strictly speaking'; it is precisely because of what he saw as the generic nature of novel discourse
For Bakhtin, Saussure's opposition between the abstract or systematic langue and the concrete individualistic parole belies an understanding of language as a living, diversified construct between living, diversified speakers; language as 'utterance' in a sociat and historicat context:
at any given moment of its historical existence, language is heteroglot from top to bottom: it represents the co-existence of socio-ideological contradictions between the present and the past between differing epochs of the past, between different socio-ideological groups in the present between tendencies, schools, circles and so forth, all given a bodily form. These 'languages' of heteroglossia intersect each other in a variety of ways, forming new socially typifying 'languages'. ('Discourse in the novel' (DIN); see Bakhtin, 1981, p. 291).