Derek Parfit, Ex-Philosopher

Or, “philosophy advances one funeral at a time“? Oddly, no-one has ever said that (<checks Google> – no, I’m right: no-one ever has) because of course it doesn’t fit. Philosophy isn’t like science, with clear progress that rather leaves the Emeritus behind it3. DP says otherwise in his magnum opus, OWM, but doesn’t prove the point.

So: news reaches me of the death of Derek Parfit, Philosopher. I am entirely unaware with his work, although the name is very vaguely familiar. Some people I respect pointed me initially at The whole philosophy community is mourning Derek Parfit. Here’s why he mattered (Vox). I read it and am unimpressed. I am then pointed to HOW TO BE GOOD: An Oxford philosopher thinks he can distill all morality into a formula. Is he right? (NY). Again, I am unimpressed. Today, finding myself surfeited of sci-fi in Waterstones, I browse his “On What Matters”, volume 1. After reading the preface, and then more-and-more rapidly skipping, I got to page 200 without finding anything of interest and stopped.

This post is to record some notes of my reactions. As you’ll see from the above, they hardly amount to a careful review by someone thoroughly familiar with his work, so if that’s what you want, go else where. They are mostly a record for myself, in case I ever wish to revisit (so why on this blog, rather than my personal one? Because the post got too long).


Section: “Why personal identity doesn’t matter”. I suppose I should warn you (if you need warning; you shouldn’t) that I’m reacting to what I read. Whether “Vox” have faithfully paraphrased his work I cannot tell; although some is directly his words. A thought experiment: we take a person (Parfit) and split his brain into two halves, implanting them in two brainless bodies we happen to have handy, and since this is a thought experiment we waive any medical implausibilities. Then “Each of the resulting people believes that he is me, seems to remember living my life, has my character, and is in every other way psychologically continuous with me,” And then proceeds to draw conclusions (of the ordinary semi-paradoxical and totally familiar from various sci-fi novels sort) from this thought experiment. However, the conclusions are only valid if the experiment is actually possible. If it isn’t1, all of the conclusions are null. So I am unable to understand why his conclusion – identity doesn’t matter – is supposed to hold in the real world.

There then follows another thought experiment (the A / A+ / B- / B one, read the link if you care about the details) which is essentially a shell game: it works only because, if you’re not careful, you fail to notice that he changes the definition of “better” (which he is careful never to write down explicitly) when making different comparisons. And all of this to get to nothing more interesting than “Z is a world with vastly, vastly more people — 100 billion, or 200 billion, say — all living lives that are just barely worth living. Parfit’s reasoning suggests that this is better than a much smaller world where people are, on average, much happier. This ludicrous-sounding suggestion…” But why is this suggestion ludicrous? It might be, if you’re a nice comfortable philosopher facing the horror of imagining just about scraping by. But if you imaging yourself as a randomly selected one of the 100 or 200 billion, facing a 93-in-100 or 193-in-200 chance of being rubbed out in the transition to a present-day-Earth-population world, it is very easy to see that you might prefer the over-populated world. So again, I fail to understand: Parfit appears to do nothing more than state a commonplace, badly, and with invalid reasoning.

Then there’s a bit about Altruism. Altruism is good, I agree. But Some of us ask how much of our wealth we rich people ought to give to these poorest people. But that question wrongly assumes that our wealth is ours to give. This wealth is legally ours. But these poorest people have much stronger moral claims to some of this wealth. We ought to transfer to these people, in ways that I mention in a note, at least ten per cent of what we earn is to my mind poorly reasoned (see OWM, below, which seemed much the same). There is more blurring of words; “ours” needs a consistent meaning if his sentences aren’t to turn into mush. He introduces 10% with no apparent justification at all. He might, perhaps, justify it from experience: the church used to claim a much-hated 10% tithe and perhaps 10% is an empirically-sanctioned balance between non-trivial and not-too-onerous.


The NY piece is, bizarrely, illustrated by DP costumed as a coal miner (or perhaps a thought experiment blew up in his face?). We start with the same two-brain thought-experiment of Vox, then we get Parfit is thought by many to be the most original moral philosopher in the English-speaking world which seems weird to me. I’d pick Hayek over DP any day. If you don’t think Hayek is a moral philosopher you aren’t thinking.

It then continues with Suppose that a scientist were to begin replacing your cells, one by one, with those of Greta Garbo at the age of thirty. At the beginning of the experiment, the recipient of the cells would clearly be you, and at the end it would clearly be Garbo, but what about in the middle? It seems implausible to suggest that you could draw a line between the two—that any single cell could make all the difference between you and not-you. How dull. This isn’t even new; it’s a version of the paradox of the heap or the ship of Theseus, but with the bonus of not actually being possible and therefore less interesting.

On What Matters

Like I say, I browsed it. The preface was a rather dull attempt to introduce his pet philosopher, Henry Sidgwick. The text… just didn’t stick in my mind, so I can tell you nothing useful about it at all. It seemed, ironically for a book entitled “On What Matters”, not to matter at all.

From the NY piece I read After Parfit finished “Reasons and Persons,” he became increasingly disturbed by how many people believed that there was no such thing as objective moral truth. This led him to write his second book, “On What Matters,” and now I read that, I do recall various places where he did, effectively / implicitly (but I do not recall explicitly) assert the existence of objective morality. This is a familiar philosophical problem, because neither pure objectivism nor pure relativism seem plausible, but I cannot recall anything he wrote that made the issue any clearer.

NY says Parfit believes that there are true answers to moral questions, just as there are to mathematical ones2. Humans can perceive these truths, through a combination of intuition and critical reasoning, but they remain true whether humans perceive them or not and this seems to be much the same as Hobbes’s precept or law of nature:

A ‘law of Nature,’ lex naturalis, is a precept or general rule found out by reason by which a man is forbidden to do that which is destructive of his life or taketh away the means of preserving the same, and to omit that by which he thinketh it may be best preserved. For, though they that speak of this subject use to confound jus and lex, ‘right’ and ‘law,’ yet they ought to be distinguished; because ‘right’ consisteth in liberty to do or to forbear, whereas ‘law’ determineth and bindeth to one of them; so that law and right differ as much as obligation and liberty; which in one and the same matter are inconsistent… consequently it is a precept or general rule of reason ‘that every man ought to endeavour peace as far as he has hope of obtaining it, and, when he cannot obtain it, that he may seek and use all helps and advantages of war.’ The first branch of which rule containeth the first and fundamental law of Nature, which is, ‘to seek peace, and follow it.’ The second, the sum of the right of Nature, which is, ‘by all means we can, to defend ourselves.’

I far prefer Hobbes’s language to DP’s.


1. FWIW, I’d go for “it isn’t”, though I’d admit that I can’t demonstrate it. Our current world doesn’t have the surgical ability to split a brain in half, transfer it to two other bodies, and have them live. Quite possibly a future world might. But I think that were it done, the two would be recognisably not two copies of the original. Also (FWIW, and since it came up on fb) I think QM effectively prohibits “copying” brains, to the level of detail that would be required to duplicate people.

2. A slippery arguement to make, when faced with things like the axiom of choice.

3. To be fair, no-one says “mathematics advances one funeral at a time either, and yet it does unquestionably advance, in much the same way as science. Is it, perhaps, less prone to the “emeritus effect”?


* Adjective Foods (XKCD)


  1. #1 Nick Barnes

    We don’t know anything like enough about how brains work to say that QM prohibits anything to do with them. However, my impression is that if you ask brain scientists they’d probably come down mostly on the side of “no, it doesn’t” (and almost all of them will, in a less-guarded moment, laugh out loud at the sort of QM nonsense that people like Roger Penrose spout about brains). Partly because minds are very robust against a number of pretty gross physical, physiological, and electrical changes to brains, in the way that QM processes tend not to be.

    [I hope I didn’t say anything that sounded like supported RP’s stuff -W]

  2. #2 Steve Bloom
    SF Bay Area

    Well, identical babies. They become different people soon enough, although often with striking similarities. As this happens all the time in the real world, presumably it’s not admissible to the philosophical realm. (Snark aside, surely he can’t have missed this?)

  3. #3 David B. Benson
    United States

    Re: footnote 2. A better choice is P = NP?

    [I’m not really familiar with that stuff -W]

  4. #4 Russell the Stout
    Distributed among multiprocessors

    Douglas Hofstadter and Daniel Dennet compiled a marvelous underrated book on these topics, The Mind’s I
    without the erroneous baggage. So did, for that matter, science fiction author David Brin in his slyly funny Kiln People.
    Parfit’s assertion that the unborn regret not living is when I began having the fits.

  5. #5 Phil Hays

    “Theresa May has denied the government’s approach to Brexit is muddled”

    Translation seems to be: “Yes, we don’t have a clue”.

    But Brexit is Brexit. That’s clear. Right.

    Somewhere, there is a Putin smiling.

    [It does seem to be coming clearer that TM does indeed not have a clue. Silence can only be mistaken for wisdom for so long. The Economist isn’t terribly happy: -W]

  6. #6 ...and Then There's Physics

    Happened to notice this article in my Twitter feed today and thought of this post :-) . I will admit that I haven’t yet read it.

    [As expected, a philosopher defending “his patch” from the scientists doesn’t get very far before he tries to talk about science and fails miserably: several advanced scientific discoveries do in fact contradict information we receive from our senses. Einstein discovered that there’s no such thing as absolute simultaneity, for example. You’d have thought they’d do at least some basic checking before hitting “publish” -W]

    [And as for bringing in Kant to relativity: how can you do that without pointing out that K incorrectly thought space could a priori known to be Euclidean? And not only that, but all philosophers failed to point out the error in his reasoning? -W]

    [Also And then there’s the development of formal logic, which was devised by philosophers a little over 100 years ago, attempting to co-opt formal logic to philosophy, is dishonest. It would I think be more accurate to describe it as path of mathematics; though the boundaries blur. But to baldy claim it for philosophy is just lies. It would be like claiming relativity for philosophy just because in certain lights you can view Einstein (errm, and others) as philosophers rather than mathematical physicists -W]

  7. #7 William M. Connolley

    Note to anyone tempted to comment here: please do.

    One of the reasons for writing this post was to provoke people who do think Parfit worthwhile to point out the worthwhile stuff he’s done that I’ve missed, or to point out the errors in my analysis. Because if there *aren’t* reasonably obvious errors in my analysis, then all the praise heaped on DP is vacuous, and the people doing the praising are idiots.

  8. #8 ...and Then There's Physics

    [doesn’t get very far before he tries to talk about science and fails miserably]

    This is certainly something I’ve encountered a few times from those who claim to be studying scientists, or the scientific method, the history/philosophy of science. It seems quite common for such people to blunder spectacularly when trying to explain science itself, and to then somehow defend themselves by claiming that their critics (often scientists) don’t understand the history of science, or the philosophy of science, etc.

  9. #9 has

    If science evolved from philosophy, why are there still philosophers? Tenure, presumably.

  10. #10 Mark
    New York, NY


    Parfit’s masterpiece is his book Reasons and Persons (not On What Matters). I have objections to / skepticism about some of the arguments, but I also found many of the arguments challenging and persuasive. I would recommend reading that if you are sufficiently interested (I don’t think it would be worthwhile just to skim, though).

    Regarding personal identity, I would recommend reading his 1971 essay Personal Identity for the basic arguments in his words.

  11. #11 Mark
    New York, NY

    Also, I do find it helpful to use thought experiments that are possible (although I think it’s a major error to assume that’s a necessary criterion, but that’s another topic). As such, I found it helpful that Parfit’s essay Personal Identity uses the example of a severe epilepsy sufferers whose brains have been split in two, resulting in two separate spheres of consciousness.

    I would caution that Parfit’s work is often misrepresented when it is explained secondhand. The original works I mentioned my the prior post are more helpful for understanding his ideas and arguments.


  12. #12 David B. Benson
    United States

    I suppose the reference to formal logic being at bit over 100 years old is saying Bertrand Russell without actually saying so. Certainly a philosopher and not trained well in mathematics, as his opus magnum demonstrates. Indeed the following great logicians were considered philosophers, Kurt Godel chief among them.

    However, Brower was a mathematician whose so-called intuitionistic logic has had a profound influence in both mathematics and philosophy. Go over to the University and ask Peter Johnstone about topos theory; it is the flowering of that logic.

  13. #13 David B. Benson
    United States
  14. #14 Dunc

    Our current world doesn’t have the surgical ability to split a brain in half, transfer it to two other bodies, and have them live. Quite possibly a future world might. But I think that were it done, the two would be recognisably not two copies of the original.

    No, but we do have the ability to split the two hemispheres of the brain and leave them where they are, and doing this fairly clearly shows that the two are not copies of the original, because many functions are localised to one or other hemisphere.

  15. #15 Fergus Brown
    A cul de sac just off Heidegger Avenue

    I was once a philosopher (of a kind). Never heard of this chap. I’m sure he was a lovely person and will be sorely missed, but I’m not aware of anything which indicates that Vox’s principle assertion – that he matters – is true of more than a few people who knew or studied with him.
    I always felt that the limits of my philosophical competence is defined by the limitations in my mathematics. Many ‘important’ philosophers are also better than average mathematicians. You can understand why is moved more into moral philosophy/Ethics.
    Reading this post gives me the impression that the work referred to is not a good example of what philosophy can do. Others should be cautious to conclude that this is as good as it gets – it’s really a lot smarter than that, most of the time.
    Side note – whether or not personal identity matters is not interesting. Whether it can have meaning without reference to Others is, IMO.

  16. #16 Arthur Smith

    William, I think it is fairly trivial to prove that we aren’t idiots on your own terms: you imply that at the time of the New Yorker in 2011, Hayek was an important philosopher in the English-speaking world. I believe he was actually Austrian, and dead. :)

    [Hayek spoke and worked in the English speaking world. And I’d interpreted Parfit is thought by many to be the most original moral philosopher in the English-speaking world to include the dead… if you only wanted the living, why not say so? -W]

    But more to the point, at the very start of “Reasons and Persns”, Parfit examines in detail several “theories” of moral behavior, first among them self-interest. And he compellingly finds them all to be, in one way or another, “self-defeating”. That is, they fail on their own terms. Self interest may require us to behave irrationally in ways that will actually defeat our self-interest. His example of imposed slavery on a desert island under threat is a perfectly realistic if slightly farcical situation that clearly illusttrates this point.

    [OKaaaayyyy, maybe; but simply saying something is “compelling” isn’t; do you perhaps any links to pithy expositions of his arguments? -W]

    On the “repugnant conclusion” there is actually some math backing this up – the assumption of an additive utility function as a measure of value along with an innate value to a “life barely worth living”.

    [My wife pointed out that the version I was looking at (whilst it appears to be his, and broken) can be dramatically simplified, probably to the version that you’re thinking of. But the problem is it simplifies to the totally dull and non-novel “strict utilitarianism leads to unfortunate conclusions”. So I’m baffled that anyone would present it as a contribution that DP has made -W]

    The identity problems are obviously very ancient in philosophy – “cogito ergo sum” and all that. Parfit seems to have concluded that personal identity is more or less an illusion, that we have no significantly greater connection to our future or past selves than we do to other people’s identities. To me this is obviously wrong, but his strong arguments on the subject do very clearly indicate that physicalism (that identity is somehow defined by the physical state of our brains) cannot be true and there must be some form of dualism at work. Which makes many people uncomfortable.

    [I, unlike (I think) you am an atheism and would probably consider myself a physicalist, if I was sure of what it meant. Assuming it means your brackets, then yes, depending of course on what you mean by identity. Once again, it would be nice to see an exposition of these strong arguments. Don’t just say “read the book” because I’ve already tried reading his stuff, and found nothing of value, nor do I find anyone saying “oh, but you missed that bit”. If all the bits I read are of no value, and people say “try this other bit”, then I’m prepared to if its easy, but not if hard -W]

  17. #17 Arthur Smith

    Well, you put in the title of this post “ex-philosopher”, so by your own terms Hayek in 2011 was an “ex-philosopher”… I definitely find Parfit much more interesting than Hayek; though haven’t read much Hayek to be honest. (Doesn’t Hayek boil down to “freedom is good” which is pretty trivial and dull?)

    [Strangely enough, there is more to Hayek than that. Perhaps his principle contention is that a planned economy is not possible because no central planner can have the information required to do the planning. Or that price is important not for the profits but for the signalling -W]

    I found Parfit’s arguments comparable in some ways to Hobbes, as attempting to argue on as general grounds as possible, but coming from an atheist standpoint which I would think you would appreciate.

    Yes “strict utilitarianism leads to unfortunate conclusions”, but Parfit’s argument was for much more general forms of “utility” and measures of goodness than I think had normally been considered in the past. In discussing his “repugnant conclusion” he considers a lot of different ways to measure goodness – perhaps population above a certain level does not really add to total value for example, or perhaps what matters is average happiness rather than total, or other non-additive measures. He then shows that each of these alternatives has serious problems of its own, self-contradicions, etc.

    If you are looking for good summaries in other people’s words of Parfit’s arguments, the Stanford Encyclopedia of Philosophy is probably a good place to start – for example this section:
    Parfit’s ideas are also discussed in section 4 and 6 on that page. A search for Parfit will bring up many other relevant discussions there.

    [#IDM starts with the standard two-brains stuff. I’ve explained why I find that unconvincing, and as far as I know no-one has attempted to defend it. Stanford appears to not even notice the problem. So, once again I’m afraid I find the sources you propose unconvincing and problematic. Perhaps you could attempt to rebut my attack, instead of just referring to essential-duplicate-statements of the case? -W]

  18. #18 Arthur Smith

    And here’s a brief discussion of rationally induced irrationality with another example from Parfit:

    [It is kinda cute, but not really of any significance. Firstly, it fails on its own terms: the robber has no way of knowing that Moe has consumed such a drug; indeed, given the unlikelihood of it, it is rational for the robber to assume that Moe is only play-acting, and therefore to shoot one of the children in order to force Moe to stop pissing around. It is also mostly mis-described: the drug doesn’t need to induce irrationality; all it needs to induce is manifest inability to respond to threats; simple unconciousness would be more effective. Unconcsiousness would also not be subject to the flaw I’ve pointed out.

    Also, there are better examples, of which anger is one (or, perhaps, Trump versus Obama is another). *Acting* irrationally may be of advantage in negotiations. But I can’t see anything DP is saying that much matters -W]

    [BTW, I should add: my thanks for the links and perhaps my apologies for pushing this harder than is really polite -W]

  19. #19 Hank Roberts
    at the reference desk, again

    So who’s your favorite philosopher?

    [Hobbes. Surely you can tell -W]

    I recommend an economist, Carlo M. Cipolla

  20. #20 Fergus Brown
    At the Zen Cafe

    Raymond Smullyan, hands down :)

  21. #21 Arthur Smith

    I don’t quite know why so many have latched on to the split brain illustration, it’s not something I found particularly compelling when reading him, the Star Trek transporter example was I thought a better case (or generally if one could ever theoretically duplicate a human being in all essential respects, however it could be done). But the split brain example suffices for the point.

    [It is clearly a compelling *image* – every exposition of his work that anyone has ever pointed me at seems to start with it. As a useful starting point for discussion I don’t see it as helpful -W]

    Which is rhat, over the course of a lifetime, we humans seem able to have a continuous identity that survives a variety of assaults on our bodies, and much change in our brains, our personalities, our relationships with the world around us. Every atom in our bodies is replaced over time. From the reductionist/physicalist viewpoint, somehow that continuously changing physical system maps to or creates in itself an “I” that seems to be a single thing – the identity. How does that mapping work, or is it just an illusion of some sort?

    [Ah, now that is a much better way of putting it. And it is the way that we (my family: we did DP as a topic-for-conversation-over-Sunday-dinner) ended up talking about it. Put that way, my answer is that you should thing in terms of objects in spacetime, and our “identity” is the long blob that starts at birth and ends at death. Clearly, there is continuity there despite replacement and growth. And clearly what matters there is not the raw physical continuity: so if you were, magically, Star-Trek transporter style, able to xfer the structure to a remote location (though as I say I think QM makes this impossible) – whether you destroy the original or not – then the “personality” is continuous -W]

    The split-brain problem is an example of an assault on that physical system that nevertheless potentially allows continuity of identity – at the least it (if it were possible) allows continuity of conscious life in some form. So surely from the perspective of the 2 brain recipients, they have memories going back into that time when they were one person. But now they are two. Identity can fork – and perhaps does already in the cases Dunc mentioned, though it is hard to tell from the outside I expect.

    [Pfft, then if you allow the theoretical possibility then identity can fork – so what? -W]

    This is only one of many explorations Parfit made of the problems with identity from a reductionist viewpoint. Much more entertaining than Hobbes I thought…

    [Not if you’re interested in governance :-) -W]

  22. #22 David B. Benson
    United States

    Hobbes? Even Raymond Smullyan is better.

    I’m quite taken with some of Epicurus myself…

  23. #23 Arthur Smith

    Well forking identity matters if identity itself matters, as it does for most attempts at building ethics. For example, how do you handle self-interest, if the self can split?

    [In the obvious way -W]

    Do you still put the interest of your other “self” first,

    [No, of course not -W]

    or equal with “yours”?

    [No, why would you? -W]

    Or is it more a sort of family relationship?

    [Essentially, yes -W]

    Suppose the person commits a serious crime before the split – do both future selves need to receive the same punishment?

    [Yes -W]

    Do you cut the prison term in half?

    [No. Are you missing the point that while the two post-split personalities are the joint inheritors of the pre-split, they will inevitably diverge. They aren’t the same person -W]

    How does ownership of prosperity work if the owner can split into several separate beings?

    [Failing any explicit contract otherwise, both halves have joint ownership -W]

    Etc. the point is, the self – identity – is central to almost everything we think about regarding right and wrong. But if it’s more an illusion then what does that imply….?

    [Ah. Suddenly you’ve taken a step I don’t understand: where did “an illusion” come from? Everything you said before then, all the questions you asked, had answers that just seem bleedin’ obvious and not deep at all. Then, suddenly, you go completely off the rails. Are you following DP in that? -W]

    And the arguments in this regard are based on much more than just the splitting problem. Should I sacrifice now so I can enjoy the fruits of that sacrifice later? But am I really the same person later that I am now? Etc.

    [That’s just discounting. Is there any hint that DP understands discounting? -W]

  24. #24 Arthur Smith

    By the way, I wouldn’t say Parfit is my favorite modern philosopher, though he is one of the ones I have enjoyed most. Douglas Hofstadter is always provocatively entertaining in his leaps around the subject of what an “I” is, which he’s trying to turn into a real artificial intelligence project. I’ve read Daniel Dennett on the problem of “consciousness” which is I think essentially the same question – interesting arguments based on real brain science but I think he stretches too much and glosses over the aspects that are really central to our experience. Steven Pinker was interesting on some questions of innateness but he seems to have turned into a conservative apologist lately. Lee Smolin has written some stuff about fundamental physical concepts (like time and the possible nature of physical laws) but in his latest book he seems to have recruited a random philosopher who added in my mind almost nothing to the discussion (Smolin’s portions of the book seemed original, the philosopher’s just repetitive). So the people I really like who write on philosophical topics these days probably aren’t strictly philosophers themselves. I did like Philip Kitcher’s book on how science survives its bad actors (he is a philosopher of science). And of course I’ve read Kuhn and Popper. Popper’s arguments were very physics-oriented which was nice for me to read about, but maybe led him astray…

    [I don’t recall much of TOSAIE being physics orientated. DH’s GEB was good, and introduced me to a number on concepts. I particularly liked the idea that a sufficiently advanced AI might be bad at arithmetic -W]

  25. #25 Arthur Smith

    Well, perhaps I haven’t represented the essential questions here well. I did find another Stanford encyclopedia article that I think has a better discussion of the split-brain problem here:
    (section 5: fission). Maybe the real thing that bothers people is to imagine this process happening to themselves. What is the subjective implication. Surely only one of the future copies of yourself is really “you” – people don’t have the experience of being in two separate bodies at once, nor would they under any normal physical/reductionist viewpoint. But do both copies have the same subjective experience? Objectively, assuming a perfect copying process, or equal amounts of damage in each copy, there’s nothing to believe one copy over the other. So where there was once only one “I”, now somehow there are two. Perhaps it’s not paradoxical from certain viewpoints, but it seems to be subjectively to be a very strange thing to assert. And yet it seems also to be something that really could happen…

    [Unfortunately, I don’t really see the problem here. If you do the split (via, say, the magical and IMHO impossible Star-Trek transporter beam) then both copies are you. Both copies have the same subjective experience before the split – by definition – but different thereafter. I think there’s a degree of confusion around the “things equal to the same thing are equal to each other” question; but this isn’t maths. Before, there is one “I”, be definition. That “I” is continuous with each copy. Each copy is continuous with the original. The join of “original and copy” is an “I” for either copy. It is not meaningful to think of joining the copies to each other -W]

  26. #26 Kevin O'Neill
    United States

    WC writes: “[That’s just discounting. Is there any hint that DP understands discounting? -W]”

    Is it? In what sense is the WC of 30 years ago the same WC of today? If they are not the same, then should the same model of discounting be applied as when they are the same?

    I don’t believe there is a simple answer to the question of self. It can only be answered on a case by case basis. If people can significantly change, then it becomes rather meaningless to say that the pre-change John Doe is the same person as the post-change John Doe. This is especially true in cases of severe trauma.

    [Yes. But we’re not talking about cases of severe trauma. The assumption is that the splitting is trauma-free -W]

    The physical body may have a continuous existence retaining the same fingerprints, retinal patterns, etc – but in many if not most other respects the person we once knew is gone – completely – and a new person occupies the physical shell.

    I’ve always thought it funny that I hate cottage cheese. Every year or two I’ll try a small forkful just to remind myself or reverify that I hate it. What makes it funny is that one of my earliest memories from probably around age 3 is wolfing down half a carton of cottage cheese at the dinner table and being scolded by my mother to leave some for others. I have memories of that person, but I am not him.

  27. #27 Russell Seitz
    Cambridge MA


    how do you know you don’t mean Smullyan’s twin brother ?

  28. #28 Marcos Alvarado


    If you were a philosopher in the sense that you studied it academically and did research in the field, I’m shocked you’ve never studied Parfit. I ran across him several times and I only studied philosophy at the undergraduate level. Not sure what other ways there are of being a philosopher but they’re irrelevant IMO if your point was “I was a philosopher and I’ve never heard of him so he must not be important”, which seems like it was. No offense meant.

  29. #29 David B. Benson
    United States

    Having taken a course in psychobiology from Roger Sperry with Mike Gazeniga as TA, I note that, as mentioned above, left -right split brains, severing the corpus collosum, does not lead to two copies of one individual.

    So I find all this discussion unscientifically silly. Shall we go on with the important question of how many angels will fit on the head of a pin?

  30. #30 David B. Benson


    Stupid spelling corrector on this device…

  31. #31 izen

    Sill the best exposition of the problem of existence and identity around I think. Even deals with the morality of it all…

  32. #32 Arthur Smith

    izen- great video, exactly on point, I think it’s illustrating very close to a scenario Parfit described in detail (a trip to Mars where the transport machine malfunctions).

    William – on discount rates etc – in Reasons and Persons Parfit has an entire chapter (8) on our attitudes towards time, and section 62 (among some others) discusses discounting explicitly. Is exponential discounting rational? Maybe some other functional form is closer to what people actually do. Is nearness in itself important, or is it just a matter of likelihood of receiving the reward? Shouldn’t we overweight the likely desires of our later lives, when we will surely be wiser? So yes, discounting is definitleky on the table here.

  33. #33 Fergus Brown
    Beyond Far Rockaway

    @27: You could always call him and ask -last time I checked he was still going strong and living in upstate NY, and occasionally doing piano recitals.
    @28: Marcos, almost by definition a degree in Philosophy needs to be selective, there’s just too much to cover otherwise, unless you make a career of it. My degree didn’t cover him, but considering it began the year that ‘Reasons and Persons’ was first published, that’s not a huge surprise. My Ethics lecturer’s flair of the day was Singer, the rest was mostly Kant and since.
    Mainly, I’m a Levinasian, of sorts.

  34. #34 Hank Roberts
    at the reference desk, again

    Just because no discussion of philosophy is compete without:

    [To be fair, the Sokal stuff was social studies, not philosophy -W]

  35. #36 Hank Roberts
    at the reference desk, again
    2017/01/12 quotes Hobbes, by the way:

    “Where there is no speech, there is no truth or falsehood.”

    That’s from

    [Book one is setting-the-scene stuff. It is part of Hobbes’s axiomatisation of human behaviour. Book two is the important one -W]

  36. #37 Alex Leibowitz

    I don’t understand Parfit’s argument very well, either, and I studied him at various points. Not as carefully as I should have, I suppose. I did find his work to suffer from the sort of tergid, far-fetched, and yet annoyingly over-precise quality that I found when reading many other analytical philosophers.

    My problem with his argument about identity is that it didn’t take consciousness seriously enough. I figure that I have to be conscious of myself as one self (a point Kant tried to articulate ad nauseaum) if I’m conscious at all, and that I have to be conscious to exist, at least in any way that matters to me — so if my brain were split, I just don’t see how the “who am I” question would come up from my perspective. I would still be conscious of myself as myself, if I were conscious at all.

    Derek Parfit was someone a lot of people liked and a lot of people liked to cite, but I didn’t find him any more inspiring than any of the other big name people I had to read while I was grinding away at my essays.