Is a person's survival different from, and more important than,a person's continuing identity?

Yes, it is.  But that is only because the notion of "personal identity" across time is traditionally interpreted in terms of "diachronic logical identity".  And the notion of "diachronic logical identity"contains unavoidable contradictions.  The concept of "personal survival", however, can be better understood as "The same person as" in a manner that it avoids the contradictions inherent in "logical identity" across time.

There are two different concepts that are called "identity".  One is "qualitative identity" and the other is "numerical identity".  Any two things A and B are said to be qualitatively identical if they are duplicates - if they are exactly similar in all respects, have all qualitative properties in common.  An example of this might be two seperate hydrogen atoms (in the same quantum state).  Less exactly, two glasses or two forks off the same assembly line would be called qualitatively identical when they are casually indiscernible.  On the other hand, A and B are said to be numerically identical if A and B are one and the same thing - if there is only one thing variously called "A" or "B".  As one famous example, Hesperus and Phosphorus are both different names for the same planetary body - Venus.  So Hesperus is numerically identical with Phosphorus (and with Venus).

The logical concept of numerical identity is normally defined as the binary relation that holds only between a thing and itself.  Logical identity is transitive, symmetric, and reflexive.  It is an axiom of most modal logics(1) that for all x and y, if x = y then necessarily y = x.  That is, identity does not hold contingently, but of necessity.  The concept of logical identity can therefore be characterized as:

• reflexive (A is necessarily identical to A);
• symmetrical (if A is identical to B, then B is identical to A);
• transitive (if A is identical to B, and B is identical to C, then A is identical to C and C is identical to A);
• necessary (if A is identical to B, then necessarily A is identical to B); and
• obeys Leibniz' Law (for any A and B, if A is identical to B then A and B have all the same properties.)  This is also known as "The indiscernibility of identicals"and is usually employed in its contra-positive form - if something is true of A and not true of B then A is not identical to B (ie. "if p then q; not-q, therefore not-p"- a modus tollens argument).

The concept of numerical identity is also discussed in two different temporal contexts.  There is "synchronic identity" and there is "diachronic identity".  By synchronic identity is meant a numerical identity holding at a single time - as between Hesperus and Phosphorus, or between Obama and "The 44th President".  By diachronic identity is meant an identity holding between something existing at one time and something existing at another - as in a person's continuing identity over time.

But the concept of diachronic identity contains a serious puzzle.  Irving Copi(2) once described the puzzle of diachronic identity by observing that these two statements both seem true but appear inconsistent:

(a) if a changing thing really changes, there can't literally be one and the same thing before and after the change;

(b) if a changing thing remains one and the same thing throughout the change, then it can not really have changed.

For any concrete particular in the world, given any time interval no matter how short, there is always the possibility (if not the inevitability) of some sort of change.  A chunk of granite, for example, an iconic image of stability, can change over a "planck interval"(3) through the decay of one of its radioactive constituents (all granites contain small amounts of uranium).  Hence the concept of diachronic identity faces this challenge - how to allow for inevitable change while retaining the defining characteristics of logical numerical identity.  A theory of diachronic identity, therefore, is an attempt to explain what it is that makes an existent at one time numerically identical with an existent at another time, while allowing for the inevitable changes that take place over time.  Typically this is done by giving necessary and sufficient conditions that are both informative and explanatory.

When it comes to personal identity, there are a number of different approaches that have been tried.  Richard Swinburne(4), for example, offers an unabashedly dualist theory in which he claims there is a "extra fact," beyond the empirically available evidence, that determines the continuity of personal identity across time, and across "thought experimental" events.  The more popular alternative approach is one of the variations of a Psychological Continuity Theory (PCT) as first outlined by John Locke(5), and made recently popular by Sydney Shoemaker(6).  Bernard Williams(7) and Peter Unger(8) offer somewhat less popular theories based on bodily continuity.

The "thought experimental" event that challenges all of these theories is that of "fission".  Philosophers draw upon the empirical evidence from surgery and psychology experiments that appear to show that cutting the corpus callosum(9), lets the two separated hemispheres operate independently.  Extrapolating this data, the thought experiment involves taking the cerebral cortex of body A, separating the two halves, and transplanting them into the bodies of B and C.  The proposal is that the result will be two personalities, each sufficiently functional to be called persons.  The question is then which of the resulting bodies contains a person who is identical with the original A-body person.  Obviously, there are only four possible answers to the "fission" puzzle:

(i)   the B-body person,

(ii)  the C-body person,

(iii) neither (the A-body person ceases to exist), and

(iv) both (the B-body person and the C-body person are both identical with the A-body person).

Answer (iv) is universally dismissed.  If A is identical to B, and A is identical to C, then logically (because identity is transitive) it is necessary that B is identical to C - which obviously is not the case.B and C are two separate and distinct bodies in clearly different locations.  Hence the consensus that the answer is not (iv).  This despite the unarguable (hypothetical) fact that each of B and C would claim vociferously that they are the temporal continuation of A.

Because traditional "fission" thought experiments make use of brain surgery, they suffer from two potential flaws that cloud the issues.  First, they run afoul of scientific discoveries about asymmetries within the brain, and about the extension of personal psychology beyond just the cerebral hemispheres.  Hence they must stipulate, counter factually, that the two separated hemispheres are equivalent in all relevant respects, and contain all relevant aspects of psychology.  Second, the scenarios are applicable only to persons.  Hence they cloud issues of diachronic identity that are applicable to any concrete particular.  A more fitting approach for such thought experiments is, therefore, to take advantage of the science fictional Star Trek Transporter device.  The Transporter encodes whatever is being transported down to the quantum level, transmits the information to the destination, and then recreates the transported object at the destination - presumably out of virgin materials.  The original object is (normally) destroyed in the process.  According to episode scripts(10), however, Transporter accidents can result in the creation of exact duplicates - duplicates that would be qualitatively indiscernible down to the quantum level.  Such qualitative indiscernability of any transported particular would alleviate the flaws potential with the brain surgery experiments.  It would certainly make it more reasonable to suppose that there is simply no basis upon which one could prefer answer (i) to answer (ii).

If the Transporter operates properly, then Commander Riker begins transport on the planet surface, and then steps off the transporter pad on the starship.  There is no question (at least in the minds of all but a few philosophers in the audience) but that the post-transport person is the same as the pre-transport person.  Yet, if there is an "accident", and one copy of Riker (called Tomas) is left at the initial transport point while another copy (called William) arrives safely on the starship, then in the minds of many philosophers, there is a problem.  If you are on the starship and see a version of Riker step off the transporter pad, and are not aware of the copy left behind, you have no hesitation in acknowledging that the copy you are looking at (William) is the same person as the Riker that started the transport process.  On the other hand, if you are on the planet surface and see a copy of Riker left behind on the transport pad, and are not aware that there is also a copy that arrived on the starship, then you have no hesitation in acknowledging that the copy you are looking at (Tom) is the same person as the Riker that started the transport.  If there is a significant time interval before each observer learns of the existence of the second copy, then how can it be that all of a sudden neither version is the same person as the Riker that started the whole incident?   Ex hypothesi within these thought experiments, there is nothing to differentiate the transition from A to B (Riker to Thomas) from the transition from A to C (Riker to William).There is, therefore, nothing upon which to base a preference for answers (i) versus (ii).

With three of the four possible answers unacceptable to most, the fall-back position is to accept answer (iii).  In the event that A is succeeded by both B and C, then it seems necessary to maintain that neither B nor C is identical to A.  And this is accepted in the face of the (hypothetical) fact that both B and C will vociferously deny that conclusion.  On the face of it, it is a very strange conclusion.  It makes the continued existence of A dependent on factors that have nothing to do with A or the method by which A is continued.  This is counter intuitive, to say the least.  As Wiggins writes:

"What we need, if identity is what we want to elucidate, is a criterion which will stipulate that for a relation R to be constitutive of the identity of a and b, a's having R to b must be such that objects distinct from a and b are irrelevant as to whether a has R to b."(11)

And as Noonan writes:

"whether a later individual is identical to an earlier individual cannot ever merely depend upon whether there are, at the later time, any better candidates for identity with the earlier individual."(12)

Swinburne, because of the "extra fact" within his dualist theory, claims that the answer will in fact be either (i) or (ii) - but that we will not know until we perform the experiment.  This because the "extra fact" that constitutes the continuity of persons is not currently known to empirical science.  Presumably, Swinburne's "mind" is an indivisible non-material entity that will survive the brain transplant in one half of the brain or the other (or survive the Transporter malfunction in one copy of Riker or the other) - but not both.  As far as I know, Swinburne has not mentioned whether a "mind" would be successfully transported by a thoroughly materialist device like the Star Trek transporter.  So it is possible that for Swinburne, answer (iii) might be the correct one in a Transporter scenario - neither B nor C will be the same person as A.  If this is the case, then being transported is equivalent to personal death - since the "mind" will not arrive at the destination.  Certainly a position that is contrary to the audience's reception of normal Transporter use.  The other somewhat counter-intuitive consequence of Swinburne's theory is that a body changes identity when a person dies.  The post-mortem individual is not identical to the pre-mortem person.  Swinburne can say that this is because there is no person present in the post-mortem body.  But the consequence is none-the-less contrary to our normal way of speaking.

Williams, Unger, and Penelhum(14) (among others) argue that bodily continuity is a necessary (but perhaps not sufficient) component of personal diachronic identity.  When the experimental event is limited to brain surgery, these theories may appear reasonable.  But when examined in the light of the Star Trek Transporter, a serous flaw surfaces.  According to bodily continuity theorists, whatever it is that results from the transport can not be considered identical to whatever it was that began it - even when the Transporter operates normally.  All that is moved from the input side to the output side is information.  Using a Transporter is therefore equivalent to death.  This despite the general acceptance by the audience of the contrary proposition - almost all audience members experience no hesitation in accepting the plot-line requirement that the person who steps out of the Transporter is the same person as the one who stepped in.  Bodily continuity theorists would therefore have to maintain that the only acceptable answer to the "fission" puzzle is answer (iii).  Even a chunk of granite would not be identical across Transport.  This is the consequence of a more basic difficulty.  A bodily continuity theorist has to resolve how to describe the continuity of a body, given that any body is constantly changing (absorbing oxygen and excreting carbon-dioxide and water).  The bodily continuity theory, therefore, does not so much resolve the "fission" puzzle, as ignore it.

Psychological Continuity Theories take many forms, and there are deep debates over exactly how it should be expressed.  These debates are not relevant to my argument here, however, and so will not be discussed.  In particular, I will assume that the continuity of memory will assure the continuity of extended notions of personality like character, and so forth.  What I will understand by a PCT is:

(a)   B is the same person as A if and only if B is psychologically continuous with A.

(b)   B is psychologically continuous with A if and only if A and B form an overlapping series of persons who are psychologically connected.

(c)   B is psychologically connected to A if and only if A and B q-remember and q-desire the same things.

Derek Parfit(14) came up with his concept of "q-memory" to address the problem of the circularity of simple Lockean memory criteria. If B remembers being the same person as A, then that memory presupposes personal identity.  Instead of defining memories in terms of identity, therefore, Parfit defines q-memory in terms of causation.

(d) A person is said to have a q-memory if and only if
(i)   That person seems to remember the experience;
(ii)   someone had the experience; and
(iii)  the existence of the memory was caused in the right way by the experience itself.

Thus understood, a PCT nicely corresponds with our intuitions in most puzzle cases.  Person A survives "fission" thought experimental events, because in such events the necessary memory causation is maintained - whether by brain transplants or by Star Trek Transportation.

For Psychological Continuity theorists, however, all four possible answers to the "fission" puzzle are unsatisfactory.  Not just unsatisfactory, but clearly counter to our intuitions about personal survival over time.  Whatever thought experimental events might happen to me between now and then, it is clear that if I survive the events, then I will exist as a person who will argue vociferously that I (then) am identical to the I (now).  And this, in my opinion, is an indication that it is the basic concept of diachronic identity that is at fault.  Moreover, the problems infect not just the notion of personal identity, but also the temporal continuity of concrete particulars like chunks of granite.

Derek Parfit(15) recognizes this, and argues that therefore "identity" is not what matters.  A key Parfitian question is: given the choice to maintain your personal identity or your psychological continuity, which would you choose?   Given the arguments outlined above, clearly what matters is personal survival in terms of psychological continuity.  Robert Nozick(16) provides a foundation for this notion with his definition of "The Closest Continuer Theory".  According this theory:

A at time t1 is identical with B at time t2 just in case:

(i)            B is a continuer of A.

(ii)           B is a close enough continuer A. and

(iii)          B is the closest continuer of A.

Nozick insists that:

"[t]o say something is a continuer of x is not merely to say its properties are qualitatively the same as x's, or resemble them.  Rather it is to say they grow out of x's properties, are causally produced by them, are to be explained by x's earlier having had its properties, and so forth."(17)

In other words, there has to be a degree of causal connectivity between A and B.  In the context of a PCT of personal survival, this causal connectivity can best be understood in terms of Grice's "total temporary states"(tts)(18).  One tts causally gives rise to the next tts.  In the case of Transporter travel, the intermediary causal linkage is the information flow from input end to output end.  The tts of the person initiating the transport gets recreated exactly (to the quantum level) at the terminating point, and then causes the next tts - in exactly the same way that the initial tts would cause the next tts if no Transporter event intervened.  Exactly the same story could be told about the temporal survival of the block of granite, or the dual Rikers.

With regards to how close is close enough, Nozick says:

"How close something must be to x to be x, it appears, depends on the kind of entity x is, as do the dimensions along which closeness is measured. . . . Closeness, here, represents not merely the degree of causal connection, but also the qualitative closeness of what is connected, as this is judged by some weighting of dimensions and features in a similarity metric."(19)

Here we can profitably employ the notions of "relative identity" or "identity by sortal" put forward by Geach(20) and Wiggins(21).  The relative identity theory maintains that there is no such relation as absolute identity - there are only relations of relative identity.  One cannot properly assert that "A is the same as B".  One must specify (overtly, or by context) a sortal - "A is the same K as B".  The advantage of the relativity thesis is that it nicely syncs with our common sense view of things.  Whatever it is that we wish to regard, what we call it, how we identify it, will depend on how we are thinking about it - the sortal we choose to apply.  It also means that how we view an object can change according to the context of our discussion, and our changing cognitive interests.  In other words, how close is close enough is variable according to the sortal we apply, and our current cognitive interests.  We choose whether a continuer is close enough to suit our current purposes.

The Closest-Continuer Theory (CCT) also deals nicely with many of the thought experimental scenarios employed in debates about personal identity.  Especially those that involve "fission" (as in the brain transplant and Transporter accident).  Even when there are ties for closest-continuer (as in the Riker scenario), the CCT explains why it is open to debate as to which is the "proper"continuer.  It allows for some arbitrary decision making in such situations.  The CCT provides us some insight into the deeper logic of personal survival, to which more specific theories of personhood (like PCT) can be joined.  As long as these two theories allow us to diagnose our confusions about personal identity in puzzle cases they serve their function properly.

Unlike the notion of diachronic logical identity, the notion of diachronic personal survival

• is not symmetrical (both the CCT and the PCT are temporally asymmetric.  PCT when understood in terms of tss, is specifically causal, which is temporally asymmetric);
• is not transitive (Both B and C can be tied for Closest-Continuer of A, and can be causally Psychologically Continuous with A.);
• obeys a modified Leibniz' Law (for any A and B, if A is the same K as B then A and B have all the same K-relevant properties.).

When a person's survival is considered in terms of a CCT and a PCT, therefore, it becomes clear that a person's survival is different from, and more important than, a person's continuing identity.  The notion of diachronic identity, as traditionally understood, is sufficiently flawed to be rejected as a criterion of personal survival.

Notes and References

(1)   Wikipedia contributors. Identity (philosophy). Wikipedia, The Free Encyclopedia. URL=<http://en.wikipedia.org/w/index.php?title=Identity_(philosophy)&oldid=412940173>.

(2)   Gallois, Andre, "Identity Over Time", The Stanford Encyclopedia of Philosophy (Winter 2009 Edition), Edward N. Zalta (ed.), URL=<http://plato.stanford.edu/archives/win2009/entries/identity-time/>.

(3)   (5.39124 x 10**-44 secs)
Wikipedia contributors. Planck Units. Wikipedia, The Free Encyclopedia. URL=<http://en.wikipedia.org/w/index.php?title=Planck_units&oldid=414017550>.

(4)   Swinburne, Richard & Shoemaker, Sydney;   Personal Identity, Blackwell Publishing, Oxford, England, 1984. ISBN 0-631-13432-8, pgs 1-66.

(5)   Locke, John; An Essay Concerning Human Understanding, Book II, Chapter XXVII, "Of Identity and Diversity".URL=<http://enlightenment.supersaturated.com/johnlocke/BOOKIIChapterXXVII.html>

(6)   Shoemaker, Sydney & Swinburne, Richard;   Personal Identity, Blackwell Publishing, Oxford, England, 1984. ISBN 0-631-13432-8, pgs 67-132.

"Personal Identity and Memory"in The Journal of Philosophy, Vol 56. No 22 (Oct 22, 1959), pp 868-882. URL=<http://www.jstor.org/stable/2022317>.

(7)   Williams, B.A.O.; "The Self and the Future"in Personal Identity, Raymond Martin & John Barresi (eds.); Blackwell Publishing, Malden, MA. 2003. ISBN 0-631-23442-X. pgs 75-91.

"Personal Identity and Individuation"in Proceedings of the Aristotelian Society, New Series, Vol 57 (1956-1957), pp 229-252, URL=<http://www.jstor.org/stable/4544578>

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(8)   Unger, Peter; "Fission and the Focus of One's Life"in Personal Identity, Raymond Martin & John Barresi (eds.); Blackwell Publishing, Malden, MA. 2003. ISBN 0-631-23442-X. pgs 184-198.

(9)   (a thick bundle of neural fibres beneath the cortex in the eutherian brain at the longitudinal fissure that connects the left and right cerebral hemispheres and facilitates interhemispheric communication)
Wikipedia contributors. Corpus callosum. Wikipedia, The Free Encyclopedia. URL=<http://en.wikipedia.org/w/index.php?title=Corpus_callosum&oldid=414930005>.

(10)   ('second Chances" is the 150th episode of the science fiction television series Star Trek: The Next Generation. It was first broadcast on May 24, 1993. In this episode, Commander Riker comes face to face with an eerie duplicate of himself, created by a transporter phenomenon.)
Wikipedia contributors. Second Chances (Star Trek: The Next Generation). Wikipedia, The Free Encyclopedia. URL=<http://en.wikipedia.org/w/index.php?title=Second _Chances_(Star_Trek:_The_Next_Generation)&oldid=414629469>.

(11)   Wiggins, David;Sameness and Substance, Blackwell Publishing. 1980. p 96

(12)   Noonan, H.W.;   "The Only X and Y Principle"in Analysis, VOl 45, No 2 (Mar 1985), pp 78-83. URL=<http://www.jstor.org/stable/3327461>.

(13)   Penelhum, Terence; "Personal Identity, Memory, and Survival"in The Journal of Philosophy, Vol 56, No 22 (Oct 22, 1959), pp 882-903. URL=<http://www.jstor.org/stable/2022318>.

(14)   Parfit, Derek; "Personal Identity"in The Philosophical Review, Vol 80, No 1 (Jan 1971), pp 3-27. URL=<http://www.jstor.org/stable/2184309>.

(15)   Parfit, Derek; "Why Our Identity is not What Matters"in Personal Identity, Raymond Martin & John Barresi (eds.); Blackwell Publishing, Malden, MA. 2003. ISBN 0-631-23442-X. pgs 115-143.

"The Unimportance of Identity"in Personal Identity, Raymond Martin & John Barresi (eds.); Blackwell Publishing, Malden, MA. 2003. ISBN 0-631-23442-X. pgs 292-317.

(16)   Nozick, Robert; Philosophical Explanations, Harvard University Press, Cambridge, MA. 1981. ISBN 0-674-66479-5. pp 27-114.

"Personal Identity through Time"in Personal Identity, Raymond Martin & John Barresi (eds.); Blackwell Publishing, Malden, MA. 2003. ISBN 0-631-23442-X. pgs 92-114.

(17)   Nozick, Robert; Philosophical Explanations, Harvard University Press, Cambridge, MA. 1981. ISBN 0-674-66479-5. pg 216

(18)   Grice, H.P.; "Personal Identity"in Mind, New Series, Vol 50, No 200 (Oct 1941), pp330-350. URL=<http://www.jstor.org/stable/2250897>

(19)   Nozick, Robert; Philosophical Explanations, Harvard University Press, Cambridge, MA. 1981. ISBN 0-674-66479-5. pg 218

(20)   Geach, P., Reference and Generality, Cornell University Press, Ithaca, New York, 1962.

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