There are strong elements of both sociological realities in Forster's work. They play a rather definitive role in the plot structure and development. I might posit that the individual nuances of character and motivation also play a role in the plot development. I am a bit leery of the notion of "hinge" in the statement. I think that the work is complex enough that multiple and converging elements can help to advance the plot. Hanging the development of these intricacies into two conditions might be limiting. Mrs. Moore's change over the course of the novel might not be linked to race and gender as much as the changing arc of human perception. Godbole's role in the novel is challenging enough to determine so as to possible transcend the reductive elements of race and gender.