What metaphors are used in The Confessions of Nat Turner by William Styron?

The narrative can be seen as a metaphor for freedom. Freedom is an intangible concept; there are many who are never technically enslaved, and yet are not free. There are also degrees of freedom, as Nat learned throughout his life, serving under several different masters at various plantations. Under Marse Sam (Samuel Travis), for example, Nat was allowed much more freedom than he'd had under the cruel Moore. The very idea of allowing someone freedom is a false concept, though.