In “The Substance,” the cleaving works differently: An experimental drug splits users into two bodies, one young and beautiful, one middle-aged or old. They spend a week in each body while the other lies comatose. The young and old selves appear to have continuous memories (though the movie can be tantalizingly ambiguous about that), but they develop different priorities and relationships. Sue, the younger self of Elisabeth, rockets to Hollywood stardom, while Elisabeth becomes a recluse, discarded by an entertainment industry that reviles aging female bodies.
The question of what makes you “you,” from moment to moment and across a lifetime, has been a subject of intense debate among philosophers. Writing in the 17th century, John Locke emphasized continuity of memory. By his standard, each innie-and-outie pair from “Severance” constitutes two entirely different people, despite their sharing one body. Conversely, Elisabeth and Sue from “The Substance” constitute a single person because they seem to recall some of the same experiences. In contrast, the 20th-century philosopher Bernard Williams prioritized bodily continuity, a perspective that makes an innie-and-outie pair a single person but Elisabeth and Sue two distinct people. The 21st-century psychologist Nina Strohminger and the philosopher Shaun Nichols emphasize continuity of moral values, yielding more complex judgments about these fictional cases. Other scholars view selfhood as a social construct, determined by relationships and societal expectations.
Unsurprisingly, the characters themselves are confused. In “Severance,” the innies sometimes seem to regard the outies as themselves, sometimes as different people, whereas the outies seem to regard their innies with indifference or worse. Meanwhile, in “The Substance,” mature Elisabeth says of young Sue that “you are the only lovable part of me” — in a single sentence treating Sue both as other and as part of herself.
In real life, such confusion rarely arises because memory, embodiment, personality, values and relationships typically align. Both my wife and the D.M.V. can decide on sight that I’m me, even if they care more about memory, skills and responsibility over time — since they trust in the correspondence of body with mind.
Of course, even outside of science fiction, the correspondence isn’t perfect. Advanced dementia can strip away memory and personality, leaving loved ones to wonder whether the person they once knew still exists. Personality, memory and social relationships can fragment in multiple personality or dissociative identity disorder, raising the question of whether Jekyll should be held responsible for the malevolence of Hyde.
