The Vanishing Half is focused on the question of identity. The author seems to conclude that identity is not a permanent condition but a mental construct that changes over the course of a lifetime. Stella illustrates this theme more obviously than the rest of the characters in the novel. She begins life as a Black girl who experiments with passing for White. However, her decision to pass permanently is only partly due to the material advantages afforded by being White. Stella is also a twin who always felt overshadowed by Desiree’s stronger personality, and she longs to have an identity all her own. Her rejection of her family is partly because of race but partly a need for self-assertion. The identity she fabricates for the benefit of her husband and daughter does not include an identical sibling.

As much as Stella wishes to create a distinct version of herself, the effort costs her on a psychological level. She never feels a sense of belonging because the identity given to her at birth still haunts her. She imagines a conversation with her Black friend Loretta:

She imagined Loretta pushing off the box and stepping toward her. Her face frozen in awe, as if she’d seen something beautiful and familiar.