A remarkable thing about the novel is that it can incorporate almost anything--essays, short stories, mock memoirs, screenplays, emails--and remain a novel. The elasticity is also a sign that unlike, say, the epic or the ode, the novel is a living, evolving form. But if its outer limits are virtually nonexistent, the minimum requirement is generally that there be a narrative telling us something. In this way, any manner of book can find a way to justify calling itself a novel. But the label should not be worn lightly, since it invites scrutiny of the highest and most exacting kind.