Speech-act theorists (Fish, Austin, Derrida, Searle, etc.) were followed by reader-response theorists and “discourse” theorists (of whom Bahktin is a pioneer). The sense of his essays, collected for the first time under the title The Dialogic Imagination, is basically that discourse (the formal term for human language communication) is much more than the surface level of passing information from speaker (or writer) to listener (or reader). The tale of Goldilocks is more than relating what happened in the woods one day—it is “layered” or “stratified”—that is, other information is passed along, and other speech acts are performed, other discourses are taking place. For example, the writer is admitting that the reader must “imagine” a world outside the “real” physical world where the laws of physics prevail (bears don’t really live in houses and eat porridge); the writer is inviting the reader to suspend disbelief during the relating of the tale; the writer is implying that the story has a symbolic value; the writer is admitting that the story is being told from one of several points of view, etc. The “layers” of discourse, especially those residing in language choices—vocabulary, syntax, phonics, etc.—can be examined closely to expose “subconscious” discourses (social rules, beliefs, even epistemologies) taking place above and below the “surface” story-telling. Bahktin concentrates on the novel form or genre, especially Dostoevsky’s novels, as his laboratory (demonstrative of how much more complex than Goldilocks his theories are). These layers, or stratifications, of discourse are the topics of contemporary literature criticism.
In Bakhtin's thought, stratification refers to the many social discourses produced by the different strata that compose a society. Rather than consider the standard division into classes, he takes into account factors such as age, gender, activity, region, etc.
Discourse is in constant evolution within and among the strata, all the time trying to reflect real life and shared as well as personal experience. Thus, according to his theory, discourse lies outside the boundaries of any normative system. Grammar and traditional linguistics are examples of such systems.
Therefore, "stratified discourse" is language in action, the interaction of utterances in a social context. His particular interest in Dostoevsky's novels is due to the fact that, to Bakhtin, they stand for the best case-study to show that the characters' discourses achieve independence from the author.