From one day to the next, you inhabit one body; you have access to one set of memories; your personality, values and appearance hold more or less steady. Other people treat you as a single, unified person — responsible for last month’s debts, deserving punishment or reward for yesterday’s deeds, relating consistently with family, lovers, colleagues and friends. Which of these qualities is the one that makes you a single, continuous person? In ordinary life it doesn’t matter, because these components of personhood all travel together, an inseparable bundle.

But what if some of those components peeled off into alternative versions of you? It’s a striking coincidence that two much talked-about current works of popular culture — the Apple TV+ series “Severance” and the film “The Substance,” starring Demi Moore — both explore the bewildering emotional and philosophical complications of cleaving a second, separate entity off of yourself. What is the relationship between the resulting consciousnesses? What, if anything, do they owe each other? And to what degree is what we think of as our own identity, our self, just a compromise — and an unstable one, at that?

As “Severance” fans prepare for its long-awaited second season, which premieres on Friday, and “The Substance” makes its way through awards season, it’s worth considering why these two stories and the provocative questions they raise have struck such a nerve.

In “Severance,” characters voluntarily undergo a procedure that severs their workday memories from their home-life memories. At 9 each weekday morning, “severed” workers find themselves riding an elevator down to the office, with no recollection of their lives outside of work. These “innies” clock a full workday and then, at 5, ride the elevator back up, only to find themselves riding back down the next morning. Meanwhile, their “outies” come to consciousness each weekday afternoon in the upbound elevator. They live their outside lives and commute back the next morning, entirely ignorant of their innies’ work-time activities.

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.