The question asks which theorist defines the novel as:
“a phenomenon multiform in style and variform in speech and voice.”
This language points directly to the concepts of:
- polyphony
- heteroglossia
- multi-voicedness
- plurality of styles and discourses
These are signature ideas of Mikhail Bakhtin, not Forster, James, or Auerbach.
In “The Dialogic Imagination”, especially in the essays “Epic and Novel” and “Discourse in the Novel”, Bakhtin argues that the novel is:
- fundamentally multivoiced (polyphonic)
- constituted by a diversity of socio-linguistic registers (heteroglossia)
- shaped by multiple styles, discourses, and consciousnesses
A central Bakhtinian formulation is that the novel is:
- “a diversity of social speech types’’
- “a plurality of independent and unmerged voices’’
- “heterogeneous in style, variform in speech’’
The quoted phrase in the question paraphrases this exact definition.