The Retreat of Reason Part 7 pps

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THE IDENTITY OF

MATERIAL BODIES

ON our pre-reflective conception, naive somatism, we take ourselves to be identical to

our bodies because we assume that they satisfy both the ownership and the phenomenal

conditions for being the subjects of our experiences. But in fact neither our bodies nor

physical things (it has to be physical things) of any other kind play this double role. So

naïve somatism cannot be articulated into a philosophically defensible criterion of our

persistence. Still, it supplies a rough-and-ready criterion serviceable in everyday circum￾stances. According to it, our persistence consists in the persistence of a material body.

I shall now look into the notion of the persistence of such a body. Although I think that it

will emerge that this notion is probably basic and indefinable, this investigation will

throw up some findings that makes it a useful prelude to a discussion of the importance

of our identity.

A Sufficient Condition of Material Identity

I have here and there in earlier chapters assumed that the diachronic identity of a mater￾ial thing entails some sort of spatio-temporal continuity. Now, it is a commonplace that

for every material thing, m, there has to be some kind or sort, K, to which m essentially

belongs, that is, which is such that m must be a K at every time at which it exists. Is it also

the case that, if m begins to exist at a time t1 in a region r1 and ends its existence at tn in rn,

it will have to exist, as a K, at every time between t1 and tn in some series of regions linking

r1 and rn in space? Presently, we will find that this is not so: the requisite spatio-temporal

continuity is less stringent.

In the foregoing, I have employed the commonsensical framework of enduring things

that successively exist (in their ‘entirety’) at different times until they cease to exist. Such a

framework is presupposed when we speak of a thing (identified as) existing at one time

being identical to a thing (identified as) existing at another. This identity is thought to be

The Identity of Material Bodies 299

consistent with the thing undergoing a lot of changes in the course of time. Some

changes, however, rule out diachronic identity. To ask for the necessary and sufficient

conditions for m1 at t1 being identical to mn at tn is to ask: what changes between t1 and tn

are such that if and only if they occur, m1 will not be identical to mn? For instance, are

these changes precisely the ones that are incompatible with there being, at all times

between t1 and tn, something of the kind to which m1 and mn essentially belong?

The three-dimensional commonsensical framework has a rival, four-dimensional

conception that in place of the notion of a thing operates with the notion of the whole of

its existence or ‘career’. Accordingly, any shorter time during this period will be only a

‘stage’ or ‘slice’ of the thing. The thing has ‘temporal parts’, or other stages, making up its

existence at other times. In contrast to spatial parts, these temporal parts or stages seem to

be instantiations of the same kind as the thing of which they are stages, for example, a

stage of a ship or sheep is apparently itself a ship or sheep. If the duration of a ship or

sheep had been shortened from twenty years to twenty minutes, the result would still be

a ship or sheep. In this four-dimensional framework, the problem of diachronic identity

will take this form: what conditions are necessary and sufficient for different stages being

stages of the existence of one and the same more lasting thing?

The four-dimensional framework could in this fashion be used to rephrase the issue.

But it should be borne in mind that the existence of a thing is not the same as the thing

itself. For instance, a (material) thing is composed of matter, but its existence is not; its

existence has duration, but the thing itself does not. And a thing cannot be identified with

the whole of its actual existence, since the thing could have existed for a shorter, or

longer, period and still be the same thing. It follows that we need to make up our minds

whether a ‘stage’ of a thing is a shorter bit of its existence or the thing considered as exist￾ing only at this time. If, however, we are not guilty of these confusions, there may be no

harm in employing the four-dimensional framework in discussing diachronic identity.¹

It may seem that we must take the relata of the relation of diachronic identity to be

momentary, that is, the times at which things are identified to be moments, times having

no duration or extension. For if they have extension, one can distinguish an earlier and a

later part of the things existing during them which are related precisely in the manner to

be analysed. Within each of these parts, one can in turn separate an earlier and a later

part, and so on. It is only if we at last arrive at something momentary, and the analysis is

applicable to it, that we have succeeded in giving a general, non-circular analysis of what

makes a thing persist or retain its identity through time.

Unhappily, there seem to be serious problems besetting such attempts to understand

transtemporal identity or persistence in terms of relations between momentary things.²

But even if, in response to these difficulties, we scrap the notion of a momentary thing

and grant that, however far the regress is pursued, the relata will be of some, albeit very

short duration, it does not follow that the explication, though non-reductive, will be

vacuous. It can be informative to be told that two things existing at different times are

¹ But see David Oderberg who argues that “it is precisely the conflation of a persistent with its life-history which

permits the stage-theorist to give the appearance of revealing the existence of a novel ontology” (1993: 127–8).

² See Saul Kripke’s unpublished, but widely known, lectures on identity over time.

identical if and only if they stand in a certain relation R to each other, although these

relata are persisting things that in turn are divisible into things that stand in R to each

other, and so on ad infinitum. (Compare: it can be informative to be told that someone is a

human being if and only if both of his/her parents are human beings.)

At most, what we can aspire to do may well be, then, to spell out such a relation R that

makes identical two things which themselves persist for some period. As already

indicated, it is often suggested that the persistence of a material thing, m, consists in the

spatio-temporally continuous existence of something of the kind of which m essentially

is, that is, that this relation is R. Granted, since the notion under analysis is very pervasive,

it is hard to get rid of suspicions that it crops up in various places in the analysans, reducing

it to circularity. For instance, it has been argued both that the requisite place-identifications

presuppose the identity of persisting objects and that the notion of an essential kind

does.³ But, in line with the concession in the foregoing paragraph, let us waive such

worries and merely ask whether a continuity analysis along these lines could give a condi￾tion that, albeit non-reductive, is both necessary and sufficient for two persisting material

things being the same K.

An obvious, and serious, difficulty with this analysis as a necessary condition—a

difficulty to which I shall return later in this chapter—is that a thing may fall to pieces

without the thing’s identity being definitely obliterated. If so, then for m1, existing in r1 at

t1, to be the same K as mn, existing in rn at tn, there need not be a K at every time between

t1 and tn in some series of regions connecting r1 and rn.

Another difficulty for such a necessary condition concerns the matter of precisely

specifying the relevant spatial path. This is due to the fact that, from one moment to

another, a thing may lose or acquire large parts while retaining its identity: for instance, a

big branch could be chopped off a tree without its ceasing to be the same tree. This

would, of course, make it occupy a different region, even if it is immobile.⁴ Clearly, it is

indeterminate how much of a thing could be lost without it ceasing to exist. This would

be true even if the issue was a purely quantitative one of the size or mass of the parts at

stake, but it is further complicated by the fact that parts are often more or less central to a

thing (e.g. the trunk is more central to a tree than the branches).

Some have thought it paradoxical to identify, for example, a tree, T, with the tree that

exists after a branch has been chopped off it. Suppose that the branch is cut off T at t.

Then, it might be urged, the tree existing after t, T*, must be identical to an undetached

part of the tree existing before t, namely, this tree minus the branch, T  B. For all their

parts are identical. But this undetached part, T  B, is not identical to T existing before t

which possesses the additional branch, B.

I reply by denying that T* is identical to T  B rather than to T. T and T* are things of

the same kind, trees, so they can be the same thing of this kind, the same tree. In contrast,

T  B is not a tree, but a proper part of one, which T* is not. What about the claim that

T* must be identical to T  B rather than to T, since T* and T  B share all proper parts

300 Rationality and Personal Neutrality

³ See, for example Oderberg (1993: 6–10 and 50–2 respectively).

⁴ For further discussion of this difficulty, see Hirsch (1982: ch. 1).

The Identity of Material Bodies 301

(while T and T* do not)? As shown by other cases, like that of the ship of Theseus

discussed below, the fact that the parts of x at one time and of y at another are identical

does not entail that x and y are identical, even if they are of the same kind, as they are not

in the present case. If T* were identical to T  B, it could not survive the loss of a further

branch which it clearly can. Instead, T  B wholly composes T*, whereas it partly

composed T.

More fundamental is, however, the problem that a condition to the effect that there be

something of a certain material kind without any spatio-temporal interruption seems

not sufficient for the transtemporal persistence of a single material thing or body of this

kind. Sydney Shoemaker has devised a thought-experiment to this effect:⁵ he imagines

there to be both machines that instantaneously destroy tables and machines that

instantaneously create them. Suppose that a ‘table destroyer’ annihilates a given

table (along with its constituents) at t, but that a ‘table producer’ creates a qualitatively

indistinguishable table on the same spot, r, the very next moment. Then there will

continuously be a table in r, but, as Shoemaker—to my mind correctly—maintains, it will

not be one and the same table. So, a spatio-temporal continuous existence of something

of table-kind does not suffice for diachronic identity of something of this kind.

He goes on to argue that an analysis in terms of continuity “has to be replaced or

supplemented by an account in terms of causality” (1984: 241). The gist is that what is

missing in the situation envisaged is that the fact that there is a table in r just after t is

due, not to there being a table in r at t, but to the operation of an external cause, the table￾producing machine. If the table existing just after t had been the same table as the one

existing at t, one would be able to say truly that there was a table just after t because

there was one at t, and not because of any external cause. Following W. E. Johnson,

Shoemaker thinks that what is at work here is a special form of causality, “immanent

causality”, distinct from ordinary, “transeunt” causality which relates events (1984: 254).

Now, it seems to me to go against the grain to say, for example, that there being a certain

sort of table somewhere was caused by there being a similar table in the same place just

before. It seems strange to me to hold that such a static state as there being a table in r at t,

could be a cause of anything, let alone the state of there being a table in the same place

just after t. Instead, I think the full causal explanation of there being a table in r just after t

is that at (or before) t a table was placed or created in r, and just after t no cause has as yet

removed or destroyed the table in r. There is an external cause of why there begins to be a

table in r at a certain time and of why this state ends at a later time. But there is no positive

cause of there being a table in r at any intermediate time. The only causal explanation of

this seems to be, negatively, that no external cause has as yet removed or destroyed the

table. That is, the only possible causes of there being a table in r are external ones. A thing’s

persistence cannot, then, be defined in terms of any “immanent” causation internal to it.

These observations, however, suggest another way of making the continuity condi￾tion sufficient: the table existing in r at t is identical to the table existing in r just after t if

there is a table in r just after t because no external causes have removed or destroyed the

⁵ See ‘Identity, Properties, and Causality’, repr. in Shoemaker (1984).

table existing in r at t (and created or placed a table in r just after t). That is, the continued

presence of a table does not require any external cause to sustain it, but only the absence

of causes that would prevent it. I think this may capture the notion of persistence

exemplified in our sense-experience, in particular, in proprioception or the perception of

our own bodies from the inside. For instance, the experience I have of the persistence of

my body, while sitting and writing this, is of there being a body in a certain chair from one

moment to another, without this state being sustained by any external cause.

It may be objected that it is conceivable that tables causelessly cease to exist and pop

into existence. That is true, but this possibility requires that there be some discontinuity,

I think. It seems no coherent possibility that, without any cause, a table has ceased to exist

and another table has popped into existence at the very same time in the very same place.

A graver difficulty is, however, that there are two crucially different ways of ‘destroying’

tables: one that is compatible with their retaining diachronic identity and one that is not.

As already indicated, and as we shall soon see in greater detail, an artefact can be

dismantled in such a way that it can be ‘resurrected’ if the parts are properly put together

again. This means that were we to turn our sufficient condition into one that is necessary

as well, we would have to rule out this type of destruction. We would have to specify that

the relevant destruction and creation mean that a numerically distinct thing of the same

kind would exist instead. But, of course, that would be blatantly circular.

Still, despite its shortcomings the analysis proposed provides some insight. For it

brings out a difference between the continuity of a physical thing or body—that is, an

entity that possesses mass, has a tangible shape, and fills a three-dimensional region of

space—which is not causally sustained by anything external, and the continuity of other

physical entities or phenomena, like purely visual entities, for example, shadows, and audit￾ory ones, which is causally sustained by something external, namely proper things. In the

case of the latter, too, spatio-temporal continuity fails to make up a sufficient condition,

but here the extra element can probably be understood in terms of the continuity being

causally sustained by one and the same external thing. So, as in Chapter 20 I suggested

about the identity of the mind, I now suggest that the identity of these phenomena is

parasitic upon the identity of proper things which may be basic and indefinable.

To simplify matters, we might as well formulate the sufficient continuity condition at

which we have arrived in the following openly circular fashion:

(C) m1 existing at t1 in r1 is identical to mn existing at tn in rn if, at every time between t1 and

tn and in some series of regions joining r1 and rn, there is something of the same kind

as m1 and mn to which they are both identical.

The Pragmatic Dimension of Material Identity

But, as already indicated, we face the problem that (C) fails as a necessary condition.

Imagine that a ship that exists at t1 is dismantled at t2 and that the planks and so on are

stacked away. Some time later, at t3, a perfectly similar ship is built out of these. It would

302 Rationality and Personal Neutrality