identity and extrinsicness

Mind Association

Identity and ExtrinsicnessAuthor(s): Brian GarrettSource: Mind, New Series, Vol. 97, No. 385 (Jan., 1988), pp. 105-109Published by: Oxford University Press on behalf of the Mind AssociationStable URL: http://www.jstor.org/stable/2254915 .

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Identity and Extrinsicness

BRIAN GARRETT

In 'Essence, Origin and Bare Identity' (Mind, I987) Penelope Mackie analyses possible responses to a problematic set of possible worlds, and argues that our reaction to this set must be either: (i) to abandon talk of transworld identity in favour of some counterpart relation; (2) to embrace some non-trivial form of essentialism, such as the necessity of origin; (3) to reject the principle that there can be no 'bare' transworld identities or non-identities; or (4) to reject the principle that transworld identities and non-identities cannot be 'extrinsically determined'. Mackie argues for the third solution to the problem. In this note I want to discuss one of her arguments in connection with the fourth response, a response which I have endorsed elsewhere,1 and to suggest that it may not be as unattractive as she makes out.

The problem, in rough outline, is this. Suppose that in the actual world wi, an oak-tree, Oi, developed from acorn Ai at place pI. Suppose, further, that there are two other possible worlds, w2 and w3, such that in w2, OI develops from a different acorn A2 at pI, and, in w3, Oi develops from Ai, as in the actual world, but at a different place, p2. There appears to be no objection to the existence of a fourth world, w4, in which an oak-tree, 02, develops from acorn A2 at pi and another oak-tree, 03, develops from Ai at p2. (See Fig. i below.) Since 02 and 03 are clearly distinct trees, it must be the case that either Oi in w2 # 02 in w4 or OI in w3 # 03 in w4 (or both). If we want to avoid commitment to non-trivial essential properties such as the necessity of origin (which would imply, in effect, that w2 is not a possible world relative to wi) and retain talk of transworld identity then, whichever we choose, we are forced to reject either the No Bare Identities principle or the No Extrinsic Determination principle.

Either Oi in w2 # 02 in w4 or OI in w3 # 03 in w4 (or both). Suppose, for example, that Oi in w2 # 02 in w4. This non-identity is either bare (i.e. it does not supervene upon facts of any sort) or else it holds in virtue of the existence of another, equally good, candidate for identity with Oi in w4 (namely, 03). The latter explanation of the non-identity implies '. . . that although the oak tree 01 could have grown from the acorn A2 at pi and have had the material composition, appearance, and so on exemplified in w2, and although there could have been an oak tree that had all those characteristics and also had a companion growing some distance away at p2, none the less Oi could not have been like that and also have had such a companion.'2 Mackie finds this consequence 'extraordinary', and advocates rejection of the No Bare Identities principle.

1 See e.g. my critical notice of Graeme Forbes' The Metaphysics of Modality, Oxford, Oxford University Press, I985, in Philosophical Books, April I986. Note that my aim in this reply is not to criticize Mackie's own preferred solution to the problem, but is merely to counter her arguments for thinking that rejection of the No Extrinsic Determination principle is not a possible response.

2 Mackie, pp. I90-I.



io6 Brian Garrett

01 01 01 02 03

1985

1900 Al * A2 * * Al A2 * * Al

pl p2 pl p2 pl p2 pl p2

wl w2 w3 w4 (actual)

Fig. I.

However, Mackie notes that best-candidate theories have attained some degree of popularity as accounts of the identity over time of entities of various sorts (e.g. persons and artefacts), and such theories imply that transworld identities and non-identities can depend upon the absence of competing candidates.3 Mackie does not want to say that a transworld identity or non-identity can never depend upon the absence of competing candidates. But she argues that rejection of the No Extrinsic Determination principle is extraordinary as a response to the present problem because the competitor trees in w4 are causally isolated from one another (they are spatially distinct from each other, and have no causal antecedents in common).4

In the sorts of cases which have been of interest to best-candidate theorists of identity over time, however, the causal isolation requirement has been violated. Thus, consider a theorist who proposes to analyse the identity of a person over time in terms of the obtaining of the relation of non-branching psychological continuity. Imagine that, in Wx, the brain of a person A is divided and each (equipollent) hemisphere is placed in a separate body, resulting in the creation of two persons, B and C, both of whom are fully psychologically continuous with A. Since branching of the relevant sort has occurred, our best-candidate theorist will claim that A # B and A # C. But had C not existed (as in Wy), A would have continued to exist and would have been identical with the person then occupying B's body (B'), who, by the necessity and transitivity of identity, is not B. (See Fig. 2 below.) (Hence, the non-identity of B in Wx and B' in Wy parallels the non-identity of e.g. Oi in w2 and 02 in w4: in both cases, the non-identity holds in virtue of the existence of a rival candidate.)

3 See, e.g., D. Parfit, Reasons and Persons, Oxford, Oxford University Press, I984, esp. Ch. I2 Sec. I9, and S. Shoemaker, 'Personal Identity: a Materialist's Account' in S. Shoemaker and R. Swinburne, Personal Identity, Oxford, Blackwell, I984, esp. Chs I2 and I 3; and D. Wiggins, Sameness and Substance, Oxford, Blackwell, I980, Ch. 3 Sec. 3 and 4, and Longer Note 3.19.

4 Mackie, pp. I90-I.



Identity and Extrinsicness 107

B'

A A wx WY

Fig. 2.

Mackie suggests that the commitment to the extrinsicness of identity in this case may not be absurd on the grounds that B and C are not 'causally isolated'.5 Although B and C may live their lives in complete ignorance of the existence of each other, and may exert no causal influence upon each other, they are causally connected with each other, indirectly, in virtue of their individual causal connections with A. It is this lack of causal isolation which renders the commitment of best-candidate theories of identity over time to extrinsicness, non-absurd.6

How convincing is Mackie's explanation here? The commitment of (certain) best-candidate theories of personal identity over time to the consequence that B in Wx # B' in Wy, in virtue of the existence of C in Wx, is supposed to be non- absurd on the grounds that B and C are causally connected to each other, via their connections with A. But what is opaque is why that indirect causal connection between B and C should be credited with so much significance. Philosophers who think that extrinsic identity is absurd are not going to be pacified by the reflection that B and C are causally connected with A. The existence of that causal connection is irrelevant, they will claim; it is the lack of causal influence of B upon C, and vice versa, which makes the judgement that B in Wx # B' in Wy, in virtue of the existence of C in Wx, absurd. Is it not absurd to suppose that, after the destruction of A's body, the identity of the person occupying the B- body (the B-body person)7 can depend upon what happens elsewhere, perhaps in a distant region of space, at a time after the transplant operation has been carried out? The absurdity (if absurdity there be) consequent upon the fact that B can truly say, on hearing that the other transplant operation was successful: 'Thank

Mackie, pp. I9I-2. 6 Note that the best-candidate theorist of transworld identity is not committed to the claim that

in a world (w5) just like w4 except that 03 does not exist, 02 in w5 is identical to OI in w2 (cf. Mackie, pp. I85-6). Such a result appears to violate the necessity of identity since it implies that, in w4, 02 is not OI, and that, in w5, 02 is OI. Fortunately, however, the best-candidate theorist is committed only to the claim that in w5, Ox is identical to the oak-tree which develops from A2, call it '02", which he will not identify with 02. This account parallels the best-candidate theorist's treatment of identity over time: in the example of the division of persons, there is no possible world in which A = B, though there is a possible world (Wy) in which A is the person (B') there occupying B's body. Thus, it is important to note, B and C are not candidates for identity with A in the sense that there is a possible world in which one of the candidates is identical to A. Similarly, 02 and 03 are not candidates for identity with OI in the sense that there is a possible world in which one of the candidates is identical to OI. Rather, it is the hunk of matter which composes, e.g., 02, which is a candidate for being the hunk of matter which, in some possible world, e.g. w5, constitutes OI.

7 The designator 'the B-body person' is to be taken as non-rigid.



io8 Brian Garrett

goodness C "took", otherwise I wouldn't have existed', is not alleviated by the fact that B and C stand in certain causal relations to the now dead A.

Moreover, consideration of the respective commitments of the following two theories of personal identity appears to undermine Mackie's proposal. The first theory analyses personal identity over time in terms of non-branching psychological continuity. The second theory analyses personal identity over time in terms of non-branching psychological similarity. Both theories are committed to the extrinsicness of identity. Now, consider the following two scenarios.

In the first scenario, a blueprint is made of A's physical and psychological states, by a process which leaves A otherwise unaffected, and then an exact physical and psychological replica of A is created, from the blueprint, by a scientist on Mars (call the replica C). According to both theories of personal identity, A ceases to exist upon the creation of the replica (since psychological branching has occurred) and a distinct person, B, comes to occupy A's body. According to either theory it is true that, had C not existed, B would not have existed-a distinct person, B' (= A), would then have continued to occupy A's body.

In the second scenario, the occurrence of a set of entirely random events results in the spontaneous creation of an exact physical and psychological replica of A on Mars (again call the replica C). According to the second theory, A ceases to exist when the replica comes into existence (since there are now two persons exactly psychologically similar to A), and a distinct person, B, comes to occupy A's body. But on this theory it is true that, had C not existed, B would not have existed-B' (= A) would then have continued to occupy A's body.

Given that psychological continuity is a causal concept, whereas psychological similarity is not, Mackie is forced to say that the commitment to extrinsicness (i.e. commitment to the thesis that B 0 B' in virtue of the existence of the replica C, and hence to the truth of the conditional that, had C not existed, B would not have existed) is absurd in the second scenario, but not in the first. This is surely very implausible-the commitment to extrinsicness of the continuity theory is as absurd (or not) as that of the similarity theory. (Of course, the psychological similarity theory of personal identity over time is logically inadequate-the relation of non-branching (psychological) similarity is neither transitive nor congruent-but the point is that its commitment to extrinsicness does not appear, in itself, to be any more absurd than the parallel commitment of the psychological continuity theory.)

One response which Mackie could make here would be to restrict the 'causal isolation' requirement so that two candidates are regarded as causally isolated from an earlier individual if they have no matter in common with the original (or, at least, if they are not in any way physically continuous with the original). In each scenario, one of the candidates is causally isolated from the original individual, and hence in both cases the commitment to the extrinsicness of transworld identity (i.e. to the non-identity of B and B' in virtue of the existence of the replica C) is absurd.

However, apart from its ad hoc character, this response risks squeezing out theories of personal identity over time (e.g. the theory that personal identity over time is analysed in terms of non-branching psychological continuity, whether or not the relation of non-branching psychological continuity has its normal cause,



Identity and Extrinsicness IO9

i.e., the continued existence of the brain and central nervous system) which many philosophers find plausible. (Think of the beam-transporter device in the TV series Star Trek: is the transporter, when functioning normally, really a form of self-destruction, or rather, as we are inclined to regard it, simply a very fast way of travelling around the universe?)

The upshot therefore, unless more is said, is that there is no significant asymmetry between best-candidate theories of identity over time and identity across worlds in respect of the absurdity or otherwise of their respective commitments to the extrinsicness of transworld identity. The implications of this conclusion can, of course, cut in two opposing directions. Either it implies, given the absurdity of rejecting the No Extrinsic Determination principle as a solution to the problems created by worlds I-4, that all best-candidate theories are flawed, or it implies, given that the commitment to the extrinsicness of transworld identity on the part of best-candidate theories of identity over time is not absurd, that the commitment to extrinsicness of any best-candidate theory is unexceptionable.

I believe that we ought to accept the latter implication. The commitment to the extrinsicness (or relationality) of identity shows that a predicate such as 'constituting the person identical with B' does not denote a genuine property of the hunk of matter which constitutes B, and that 'constituting the oak-tree identical to 02' does not denote a genuine property of the hunk of matter of which 02 is constituted in w4. It would not, I think, be an unreasonable extension of the sense of Geach's concept of a 'mere Cambridge' property to describe such properties as mere Cambridge.8

I can see no reason to regard such a consequence as absurd.9 Indeed, if the 'causal powers' account of (genuine) propertyhood is correct, one would not expect such predicates to denote genuine properties. (Reference to such a property would surely not feature in an account of the causal potentialities of the hunk of matter which constitutes 02.) If so, we have no reason to regard the commitment to the extrinsicness of identity on the part of best-candidate theories of identity as absurd, and rejection of the No Extrinsic Determination principle constitutes a legitimate response to Mackie's puzzle.

Lincoln College, Oxford B. J. GARRETT

8 See P. T. Geach, Logic Matters, Oxford, Blackwell, I972, pp. 32I-2. 9 For more on this see my 'A Further Reply to Noonan', Analysis, I987.



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