Derek Parfit, in Reasons and Persons (1984), asks you to imagine a teletransporter. You step into a booth on Earth. A scanner records every cell. The data is beamed to Mars. A new body is assembled there from local atoms, identical down to the synapse. The Earth body is destroyed.
The person who walks out of the Mars booth has all your memories, all your intentions, your same answer to what is your name. He believes he is you. Your wife, when he returns, believes he is you. He picks up the conversations you left unfinished. He pays your mortgage.
Parfit’s question is whether he is, in fact, you. He spends roughly two hundred pages arguing that the answer is less than yes and more than no, and that this answer has consequences for almost everything we believe about prudence, morality, and the long-running project of saving for retirement.
The retirement-planning industry has not read Parfit. It should.
Parfit’s argument
The view Parfit is attacking is what he calls the further fact view of personal identity — the intuition that there is some deep, additional fact, beyond all the physical and psychological details, that makes the person on Mars the same person as the person on Earth. A soul, perhaps. A continuous self. A something that travels with you, indivisible.
His move is to show, through a long chain of carefully constructed cases, that no such further fact exists. What does exist is psychological continuity: a chain of overlapping memories, intentions, beliefs, and personality traits, linking each version of you to the version a moment before. Parfit calls this Relation R. It is the thing that actually does the work we have, historically, attributed to a soul.
The crucial property of Relation R is that it admits of degrees. You-now and you-five-minutes-ago are connected by an extremely strong chain — almost every memory, almost every intention is shared. You-now and you-five-years-ago are still strongly connected, but already there are intentions you no longer share, beliefs you have abandoned, memories that have faded. You-now and you-at-fifteen share, if you are honest, only a fragmentary thread. Some scattered images. A vague sense of where you grew up. Almost nothing else.
Push the chain out forty years and what is left? Parfit’s answer is: not nothing, but not very much. The person you will be at 75, if you make it, will share with you a name, a body that descends continuously from yours, perhaps a handful of childhood memories that have survived erosion. He will not share your current friendships (most of them dead or estranged). He will not share your current politics (recalibrated by four decades of news). He will not share your current sense of humor (the references will have rotted). He will not share your taste in food, music, books, sex, or weather. He will probably not share your current beliefs about what makes a life worth living.
Parfit’s claim is that this person is less you than the version of you in this morning’s mirror. He is more like a near relative. A cousin you have an unusual amount of inside information about.
The further fact view says: but he is still me. Parfit’s reply, across two hundred pages, is: when you press hard on what that me means, beyond Relation R, you find nothing there. The intuition is psychologically robust and metaphysically empty.
This is not nihilism. It is metaphysical bookkeeping. The bookkeeping has implications.
What this means in practice
Take Marcus, 40, a marketing director in Chicago. He earns $148,000 a year, saves $42,000 of it, and is on the standard FIRE glide path. His Vanguard projection tells him that at 65 he will have $1.8 million in today’s dollars. At 75 he will have $2.1 million. At 85 he will be fine.
The person at 75 in that projection is not Marcus. He shares Marcus’s social security number and the deed to the house. The body is on the same continuous biological thread. But the man at 75 has, by then, lost his father (already in declining health), his mother (now 71), probably one of his two closest friends, and at least one of the two romantic relationships he currently maintains. His knees do not work the way they do now. His sense of humor has migrated. He does not like the music Marcus currently likes; he likes whatever music was big when he was 35, which is the way most older listeners actually work. He has different politics, calibrated against the news of 2061, which Marcus cannot imagine.
His priorities are not Marcus’s priorities. He cares, much more than Marcus does, about being near his grandchildren — children that, in 2026, do not yet exist. He cares much less than Marcus does about the marketing job’s promotion track. He cares about pain management. He cares about whether the chair is comfortable. He cares about the quality of the light in the room.
The trip Marcus is currently saving up to take with him at 75 — the slow tour of the Hokkaido coast — is a trip the 75-year-old will not take. He will be tired. The flight will be punishing. He will defer. The next year he will defer again. He will die without having taken it. The savings will fund his nursing care, which is a different kind of expense entirely.
This is not a hypothetical pattern. It is the modal one. Look at the spending data for Americans in their seventies: it drops sharply against spending in the fifties and sixties. The travel money does not get spent on travel. The discretionary budget does not get spent on discretion. Most of it gets absorbed by housing, healthcare, and the slow accommodation of a body that no longer wants what the bank account is willing to fund.
Marcus is, in Parfit’s terms, transferring assets to a stranger who happens to share his bank account.
The retirement math implication
The standard FIRE calculation — 25× annual spending, indexed to a 30-to-40-year horizon — conflates Marcus with his future selves as if they were one continuous beneficiary. The math treats you at 40 and you at 75 as the same agent with the same interests, separated only by an index card with the years on it.
If Parfit is right, that conflation is a mistake. Not a metaphysical curiosity. A spreadsheet error.
Consider three ways to allocate the same lifetime dollars. Assume Marcus, at 40, has $400,000 and is on track to save another $42,000 a year.
| Strategy | Allocation | Beneficiary |
|---|---|---|
| Standard FIRE | Save aggressively to 55, draw 4% to 95 | Marcus at 40 → Marcus at 95 (mostly the strangers) |
| Front-loaded SuicideFire | Save lightly, retire at 47, draw 5.5% to 65, bridge to SS | Marcus at 40 → Marcus at 65 (mostly the contiguous selves) |
| Mid-loaded | Save to 52, draw 4.7% to 80, accept reduced terminal | Split |
The first strategy maximizes the assets received by the version of Marcus most weakly connected to the version of Marcus making the choice. The second strategy maximizes the assets received by the versions most strongly connected. The third splits the difference.
The FIRE community has, almost without realizing it, calibrated its math to the first strategy. The argument for doing so is rarely articulated, because it would have to take the form: I should sacrifice the desires of Marcus-now in order to fund the desires of a near relative whose desires I cannot accurately predict and who will, in many cases, not exist long enough to spend the money. Stated this baldly, almost no one would endorse it.
But stated as I should save for retirement, almost everyone does.
The case for present-you
None of this means you should empty the account. Parfit’s view is not an argument for prodigality. It is an argument for accuracy. The person at 75 is some of you. Relation R does not drop to zero. You have, on the standard view, a moderate prudential obligation to him — comparable, perhaps, to your obligation to a younger sibling whose welfare you care about but whose preferences you do not get to set.
What Parfit’s view does is correct the strength of that obligation. The standard FIRE math treats it as identical to your obligation to yourself this Tuesday. Parfit says it is not — it is fractional, and the fraction declines with distance.
Practically, this means three things.
First, the forever in 4%-rule-forever is doing more work than the math acknowledges. You are not, in any meaningful sense, the beneficiary of those late-stage drawdowns. The bequest motive, if you have one, is real, and you are entitled to it. But you should label it as such — I am saving extra to leave money to my children, or my niece, or the Sierra Club — not pretend it is for you.
Second, the SuicideFire frame is not a rejection of prudence. It is prudence aimed at the right target. The 47-to-65 Marcus is more you than the 80-to-95 Marcus. Spending on the former is, by Parfit’s lights, more prudent than spending on the latter, not less.
Third, the trip to Hokkaido is now. Not at 75. Not at 65. The 75-year-old will not take it. The 50-year-old, on a slow train along the coast in November, with knees that still work and a budget that still bends, will.
Closing
Parfit died in 2017. He had been at All Souls College, Oxford, for nearly fifty years. In the last decade of his life he worked, somewhat obsessively, on a book about ethics he did not finish. People who knew him said he had become, in his late seventies, a person his younger colleagues did not entirely recognize. He himself, in the few interviews he gave, spoke about his earlier work as if it had been written by someone else. He used the third person about himself, then corrected himself, then used it again.
The 75-year-old in your retirement projection is a person you do not yet know and will not, when you meet him, fully recognize. You are entitled to leave him money. You are not entitled to mistake him for yourself.
Calibrate the math accordingly. The stranger can fend for himself.
Leave a Reply