Particular Reidentification Fred I. Dretske Philosophy of Science, Vol. 31, No. 2. (Apr., 1964), pp. 133-142. Stable URL: http://links.jstor.org/sici?sici=0031-8248%28196404%2931%3A2%3C133%3APR%3E2.0.CO%3B2-A Philosophy of Science is currently published by The University of Chicago Press.
Your use of the JSTOR archive indicates your acceptance of JSTOR's Terms and Conditions of Use, available at http://www.jstor.org/about/terms.html. JSTOR's Terms and Conditions of Use provides, in part, that unless you have obtained prior permission, you may not download an entire issue of a journal or multiple copies of articles, and you may use content in the JSTOR archive only for your personal, non-commercial use. Please contact the publisher regarding any further use of this work. Publisher contact information may be obtained at http://www.jstor.org/journals/ucpress.html. Each copy of any part of a JSTOR transmission must contain the same copyright notice that appears on the screen or printed page of such transmission.
JSTOR is an independent not-for-profit organization dedicated to and preserving a digital archive of scholarly journals. For more information regarding JSTOR, please contact
[email protected].
http://www.jstor.org Fri May 18 08:38:51 2007
PARTICULAR REIDENTIFICATION* FRED I. DRETSKE University of Wiscotisin A certain dilemma is inherent in relational accounts of space and time. If any objects endure through change, then temporal elements other than relations are required to describe them. If, on the other hand, no objects endure through change, no permanent reference system is available in terms of which to define the "same place" at different times. An argument which, by exploiting this latter difficulty, attempts to show that "objects with some endurance through time" must be accepted as fundamental is examined and found inconclusive. A sketch is then given of an alternative scheme which does allow the relevant spatial comparisons, but which does not countenance the reidentification of particulars. The discussion is intended to show that the relationist can, as indeed he must, deny the second horn of this delemma.
I. A Dilemma. Relational views of space and time yield, or can be made to yield, several interesting dilemmas. One of these lends itself particularly well to the present topic since it springs from the nature of those entities exemplifying the spatial relations. Although relationists have disagreed on the precise character of these entities, it will suffice, for the purpose of stating the dilemma, to consider them (hereafter referred to as "particulars" or "objects") in respect of their spatial attributes a1one.l A discussion of their other properties will be deferred until later. One horn of the dilemma may be put in the following way: if some particulars persist through change, then they undergo an alteration in their relational proper tie^.^ For example, the object A is beneath B and then (later) to the right of B (and beneath C). In such cases it is true to say that A is (untensed) beneath B and that A is (untensed) not beneath B. Lacking such devices as tensed predication, however, the relational idiom does not afford a consistent means of describing this sort of change. We must somehow indicate that A's being beneath B and A's not being beneath B occur at different times, and this must be expressed in relational terms alone. But A does not precede B, nor does B precede A3; neither does "beneath" precede "not beneath"-whatever that might mean. Even if we could say that A's being beneath B precedes A's not being beneath B (thus using something besides particulars-the terms for the spatial relations-as the terms for the temporal relations), the formal inconsistency remains: A is beneath B and A is not beneath B.
*
Received November, 1961. Some philosophers (Russell, Whitehead, et. al.) have, at various times, preferred to speak of "events" instead of particulars. Since, however, these "events" were taken as the terms for the spatial relations, they would be comprehended within the present notion of a particular. Although this dilemma could be stated by using any attribute which particulars might possess, change of place (motion) will alone be considered in keeping with the decision to treat particulars, for the present, simply as spatial entities. The relational properties in question are, for example, "to the left of B", "to the right of C". A change in the relation or a change in the term of this relation (B or C) constitutes a change in the relational property. The first horn of this dilemma is largely taken from Gustav Bergmann's "Some Reflections on Time," reprinted in Meaning and Existence (RiIadison, Wis.; 1960), pp. 225-263. In this example A and B are contemporaneous. The introduction of special relations (e.g., "temporal overlap," "extending over in time") would not alleviate the difficulty since, whatever their relationship in this respect might be, A is still beneath and not beneath B.
133
134
FRED I. DRETSKE
On the other hand, if no particulars persist through change, it would seem that the traditional analysis of "the same place" cannot be maintained. T h e standard relational characterization of an object, A, being in the sameplace at a later time than another object. B, consists in A's being spatially related to a given set of objects, selected as a reference group for the motion in question, in precisely the same way in which B was related to them earlier. But, and this is the expression of the other half of the dilemma, if no particulars persist through change, no reference objects of sufficiently long life are available. A reference object would, according to this analysis, necessarily change: first being related to B in a certain fashion and then to A. I t would, for example, be above B and then above A (and not above B). This, however, is ruled out by hypothesis. Therefore, if no particulars persist through change, the standard analysis of "the same place" is unsatisfactory and a new one must be found. This latter difficulty is occasionally exploited to justify the introduction, or rather retention, of continuants in one's fundamental ontology. A recent statement of this argument is given by P. F. Strawson in the first chapter of Individz~als:A n Essay in Descriptive Metaphysics (London, 1959). He purports to show that material bodies, three-dimensional objects with some endurance through time, must be the "basic" particulars in the unitary spatio-temporal framework of four dimensions with which we, in point of fact, operate (38-39). Strawson puts it as follows: Now if we are to operate the scheme of a single unified spatio-temporal system or framework of particulars, it is essential that we ... have criteria or methods of identifying a particular encountered on one occasion, or described in respect of one occasion, as the same individual as a particular encountered on another occasion, or described in respect of another occasion (31).
The argument sketched in the second half of our dilemma is, roughly, Strawson's reason for thinking that within our ordinary conceptual scheme (containing, as it does, significant expressions about the "same place" at different times) there must be an identification of at least some of those particulars encountered on, or described in respect of, different occasions. Strawson's argument is a sophisticated one and, in the light of the first horn of our dilemma, it cuts at the heart of a consistent relational view. Moreover, since it has a peculiar tendency to reappear, I think it appropriate to examine this argument with some care. I t may be worthwile to show that such arguments are based on a specious, but superficially plausible, view about the nature of spatial comparisons.
2. Conceptual Schenzes. Before examining Strawson's statement of this argument, one thing should be made clear. When anyone speaks about our conceptual scheme, as Strawson does, two things may be meant. On the one hand, in talking about our conceptual scheme one may be thinking of the particular conceptual apparatus involved, those elements, procedures, and categories which are, as a matter of common usage, employed or presupposed in everyday communication. For example, there can be little doubt that material bodies ("three dimensional objects with some endurance through time") are involved in a fundamental way in much of what we say and understand in both ordinary and scientific discourse; certain statements (e.g., "I was born in this room," "He was standing over there-next to that building") are, in point of fact, used exclusively in contexts where reidentifiable particulars are available. On the present interpretation of "conceptual scheme" it is clear that the reidentification
PARTICULAR REIDENTIFICATION
135
of some particulars (i.e., treating some particulars as the same as those encountered previously or described in respect of a previous occasion) is a necessary condition for the use of our conceptual scheme; for this is how we happen to operate, and how we happen to operate defines, in this first sense of the term, what our conceptual scheme is. Any scheme in which comparable statements could be made (spatial comparisons over temporal intervals) without involving, either explicitly or implicitly, the notion of particular reidentification would, on this account, not be our conceptual scheme. T h e second sense of "conceptual scheme," the one I take Strawson himself to be using, is on a more general level. T h e conceptual scheme refers to the type of thing that can meaningfully be said in a given system of discourse or, if you please, language game-not how, in terms of specific conceptual apparatus, it is said. Two such schemes are identical, qua conceptual schemes, if what can be said in the one can also be said in the other and vice versa. They are different, for example, not if one uses tensed predication where the other uses none, but only if the use of this mode of predication alters the descriptive capacity of one system in contrast to the other. Our conceptual scheme, in this second sense, is characterized, in one respect, by the kind of thing that can be said (not the way it is said) about the same place at different times. Any system, therefore, which refuses to acknowledge the reidentification of particulars but, nevertheless, retains as significant the relevant spatial comparisons is, in this respect and according to Strawson's own terms, the same conceptual system; it is not an "alternative scheme", nor is one who proposes it a "revisionary metaphysician." That Strawson is using "conceptual scheme" in this second, more general, sense is clear from his use of such terms as "necessary" and "essential" in regard to his argument for particular reidentification.
3. The Case For Reidentllfication. Strawson is interested in those situations where the interval between the occasions of observatioil is non-continuous-is., our observation of those objects which are said to occupy the same (or different) places is interrupted. Let us, therefore, assume in what follows that when different times, occasions, or moments are mentioned, these times are separated by an interval during which observation is interrupted. With this in mind the argument may be paraphrased thus (passages are not quotations): (1) Let us suppose that we were never willing to ascribe particular-identity to the objects with which we are, or could be, confronted on different occasions (35).
That is, suppose we were never willing to accept as literally true any statement of the form "Xis the same as Y" where "X" and "Y" represent expressions (descriptions, demonstratives, etc.) used to make identifying reference to objects with respect to different occasions; e.g., this is the same desk as the one that was here y e ~ t e r d a y . ~ An indirect argument follows. (2) T h e n we should, as it were, have the idea of a new, a different spatial system for each new continuous stretch of observation . . . Each new system would be wholly independent of every other (35). Anyone seriously maintaining this position would, of course, be obliged to tell how, if not literally, such statements are to be interpreted (reconstructed, constructed, etc.) so as to retain their significance.
136
FRED I. DRETSKE
Strawson's point here, I take it, is that without some recognizable landmarks, without some common point of reference between the successively observed spatial systems, these systems would be as independent, spatially independent, as two coordinate systems would be if no transformation equations were available. "We cannot attach one occasion to another unless, from occasion to occasion, we can reidentify elements common to different occasions" (32). (3) If this were the case, however, then questions about the spatial relation of any one thing at any moment of its history to any other thing at any moment of its history when these moments are different, would be meaningless (31).
These questions would be meaningless because spatial comparisons make sense only if the two spatial sub-systems !i.e., the spatial frameworks associated with the occasions between which the comparison is made) are not independent, only if they are parts, in some way related, of a single system which includes them both. (4) But such questions are not meaningless. Mie do operate with a conceptual scheme which permits such spatial comparisons. "There is no doubt at all that this is our conceptual scheme" (35).
The assumption in (I) has led to this unacceptable result. Anyone who does not find this conclusion unacceptable is put into the "absurd" position of suggesting that "we do not really or should not really have the conceptual scheme that we do have; that Eve do not really, or should not really, mean what we think we mean, what we do mean" (35). Therefore, since the denial of (I) is a necessary condition for our having the scheme we do have, (5) 'inre must be willing to ascribe particular-identity in at least some cases of noncontinuous observation.
T h e argument may be summarized thus: common discourse embodies meaningful expressions about the relative location of objects even when the times at which the objects occupy these positions are different. A necessary condition for the significance of these expressions is the incorporation of these discontinuously spatial systems into a more comprehensive system which allows intercomparison. "But the condition of having such a [comprehensive] system is precisely the condition that there should be satisfiable and commonly satisfied criteria for the identity of at least some items in one sub-system with some items in the other" (35).
4. A i3rcliminary Reply. This argument has considerable appeal, but it omits a key step. Strawson's move from (I) to (3) contains a tacit assumption that begs the entire questioi.. The inference from (1) (supposition of no particular reidentification) to the first part of (2) (idea of a new and different spatial system) is, perhaps, unobjectionable if \'ire agree to understand by "new" and "different" precisely what is implied by (1); viz., no common particulars. We must also agree that this is the only sense that has been given to "independent" in the second part of (2). Strawson has not established any s&onger sense i f independence; the two spatial subsystems which are said to be independent may, of course, be related in other ways. If this is kept in mind, Strawson's move to (3) can only be maintained by the tacit assumption that no other relationship besides that of particular-identity (if this is a
PARTICULAR REIDENTIFICATION
137
relationship) is adequate to support a spatial comparison between different occasions. Of course, if the spatial systems on each occasion are "wholly independent" as he suggests, then it would follow (by definition) that their constituent particulars could not be spatially related; but if these sub-systems are only independent in the sense of having no common particulars (which is all we have been asked to assume), then it is not obvious, at least not to me, that the inference to (3)-spatial comparisons between such systems are meaningless-is justified. At least Strawson is not entitled to assume that no other relationship can serve as an adequate foundation for the type of spatial comparison to which he calls our attention. Considerable effort has been expended in attempts to show that other relations can achieve this objective, that causal, similarity, and other relations can replace particular-identity in the analysis of statements about physical objects. If Strawson is assuming that all such attempts are futile, he should have mentioned it. Nevertheless, there is a strong presumption in Strawson's favor; one is inclined to think that if none of the objects on one occasion are the same as any of the objects on another occasion (and this includes whatever might be used as an origin for a coordinate system), then a description of the spatial relatedness of two particulars, one from each occasion, is without sense. The above reply to Strawson's argument has only revealed that alternatives are possible, that there may be other ways, besides the reidentification of particulars, for retaining the significance of the relevant spatial comparisons. In the absence of any concrete proposals, though, Strawson's conclusion seems compelling. In the following section I would like to sketch an alternative, an alternative which takes advantage of the possibilities already indicated. It is not original, but then neither is Strawson's argument.
5. An Alternative Scheme. Consider the following situation. We have an object, call it A, moving from beneath another object B. As it moves to the left another object, C, moves in from the right until it is directly below B-in precisely the same place that A originally occupied. Our point of reference, in terms of which "the same place" is defined and in ierms of which movement is said to take place, is B. Also suppose that we observe this movement for a short time at the beginning and then again near its completion. In describing this process we have clearly assumed that B (at least) endures throughout the interval during which the motion takes place; this is what provides the basis for saying that C replaced A-i.e., directly below B. Strawson's point, in terms of this example, is that if no particular is common to both periods of observation, this type of spatial comparison is impossible. If, instead of having A, B and C persist throughout the process, we had A,, B,, and C, during the first period (t,), and A,, B,, and Cn (n # 1) during the later period (t,), what basis is there for saying that C, is in the same place that A, was ? C, is directly below B,, not below B1 as A, was. The only way we could say that Cn was in the same place as A, is if we knew that B, and Bn were in the same place. This, in turn, necessitates (or so it would seem) a n e ~ - ~ o i of n treference in terms of which B, and B,, are said to be in the same place, and a regress develops. Consider, however, the following definition for two objects being in the same place. Let us suppose that no other change, besides movement, is occuring. This restriction will later be relaxed when we consider "compound" change. The "X" and "Y" represent expressions used to make identifying references to particulars situated at different times (where, as Strawson points out, these times are not ~nediatedby a period of continuous observation).
138
FRED I. DRETSKE
(6) X is in the same place as Y = dl. For all W, if W is a reference object, then if X is spatially related to W by R, then there exists a Z such that W is exactly similar to Z (in all non-spatial respects) and Y is spatially related to Z by R.s
This defines a transformation equation, of sorts, between spatial systems which have no common particulars. I t does so by specifying, roughly, that two objects occupy the same place if they are spatially related in the same way to similar sets of objects (the W's and 2's). There are several superficial objections that can be made to this definition, but they are easily answered. Strawson indicates the answers to some of them himself. For example, he points out that we are "surreptitiously thinking outside the limits of the set" when questions about the movement of the reference object arise. I n other words, questions about whether the W's and Z's are in the same place are, within the present account, without sense; they are the reference objects and "place" is defined by reference to them. Nevertheless, there are three possible criticisms which I would like to discuss briefly. In stating and answering thesecriticisrns I shall resort to a device already employed. Situations will be described in two different ways: (i) Objects shall be regarded as enduring throughout the interval between periods of observation. This, of course, reflects our common method of describing such processes, and for this purpose I shall refer to the respective objects as "A", "B", and "C" without subscripts. (ii) Objects in the second period of observation shall be regarded as numerically distinct from any object appearing in the first period. Subscripts will be used for this purpose; e.g., A,, B,, B,. My purpose is to illustrate that the second type of conceptual apparatus6 supplemented by the definition in (6), is adequate for describing those situations which Strawson thinks can only be satisfactorily described in the first way. If this can be done, the first method of description is not, as he maintains, a necessary part of our conceptual scheme; i.e., a scheme containing significant spatial comparisons over temporal intervals.
1st objection: Suppose there happened to be an identical pair of reference objects (or identical sets of reference objects). Suppose, that is, that in the ordinary way of describing this situation, there were two objects, B and D, identical in all non-spatial respects. If, then, A moved from beneath B and C moved underneath D7, the definition in (6) would place C (i.e., CT,) in the same place as A (i.e., A,) was since Certain refinements in the statement of this definition (e.g., binding the variable "R") have been neglected in order to preserve what a brief inspection will reveal to be its more or less obvious function. A clause specifying that W f Z has also been omitted because it is not important, for the present purpose, to deny that any reference object endures throughout the period in question. What is important is that this definition can be utilized whether or not this occurs-or, better, is said to occur. I shall assume, however, in the following discussion that W and Z are never the same since this is an essential part of the scheme which is to stand as a counter-example to Strawson's conclusion. Not conceptual scheme; I am attempting to show that these two modes of description constitute, in Strawson's sense of the term and in respect of spatial comparison, the same conceptual scheme. ' Complications relating to distance below are being ignored as they were earlier; their consideration would not add anything materially new and would simply the length of our examples.
PARTICULARREIDENTIFICATION
139
they are spatially related in the same way to exactly similar particulars. But, obviously, this is a m i ~ t a k e ;different ~ places are involved. This objection, in Strawson's terms, surreptitiously goes beyond the limits of our example. I t is clear that B and D cannot both be observed on each of the two occasions; for if this were the case, we would simply have two reference objects instead of one, and our definition would not lead to an incorrect result. C, would not, according to our definition, be in the same place that A, was; for A, would have moved from beneath a B-looking object (B,) and from a position, say, of beneath and to the left of a B-looking object (Dl; recall, B and D look alike); C,, on the other hand, would move into a position beneath a B-looking object (D,) and to a position beneath and to the right of a B-looking object (B,)--considerably different positions even if B and D are indistinguishable except for spatial position. Therefore, in saying that we have two identical systems of reference, the objectioil must be interpreted to mean, if it is to mean anything serious at all, that on the first occasion of observation we have one reference object (B without D) and on the second occasion another reference object (D without B). As an illustration of this suppose we are watching two airplanes and judging their position with respect to a certain star (B). During the first period of observation, one of the planes (A) appears directly below the star and the other (C) off to the right. Later, when we look again, C has replaced the first airplane (A) which has moved off to the left. In the period between observations, however, a new star (D) has become visible and the old star (B) has been obscured; we are now referring position to a different object, an object which may not, and in this case probably does not, occupy the same position as our original star. According to the proposed definition, of course, the second airplane (i.e., C,) would be said to be occupying the same position as did the first (A,). The question, then, is: isn't this a mistake ? I think it is fairly clear that this is not a mistake; at least it is not a mistake peculiar to our proposed analysis. The question is not whether our new mode of description leads to error, but whether it leads to precisely the same errors that we would commonly be led to in these circumstances (see footnote 8). The situation depicted is one in which the second airplane (C) would, if observation was limited according to hypothesis, be said to be occupying the same place as the first regardless of how we described it. This seems like a mistake only because we have, in posing the example, allowed ourselves, unlike our hypothetical viewers, to notice that a new star has replaced the old; we have placed ourselves in a position (continuous observation) to detect an event (the replacement of the old star by the new) which, by hypothesis, our viewers could not. Our definition does lead to a "mistake" then, but only because severer restrictions have been placed upon the person describing this phenomenon in the new idiom than have been placed upon the person posing the example in the old (ordinary) idiom. This is brought out clearly by the fact that we would, ordinarily, make the same mistake if observations were curtailed in the way the problem specifies.
The mistake in question is, of course, the divergence between our ordinary description and a description in terms of our definition in ( 6 ) . Since it is Strawson's contention that the lack of particular reidentification cripples the mechanism for making certain types of common spatial comparisons, the norm by which the present account is being judged is its capacity to duplicate, in these relevant respects, the ordinary idiom. Hereafter, whenever "mistake" or "error" is mentioned, it should be understood in this sense.
140
FRED I. DRETSKE
2nd objection: Contained within the definition of the "same place" is the property "reference object"; this is certainly an odd property. Even supposing that there is a set of objects which have this property, it is strange to maintain, as this definition implies, that there can be no movement within the reference group between the two occasions. The definition states that Y must have the same spatial relations to a set of similar particulars, but surely this is too strong. We do countenance certain alterations in a set of reference objects without, thereby, abandoning the possibility that, later, another object could be in the same place with respect to this reference group. According to the definition, though, any alteration within the reference group would make it imoossible for all the same soatial relations to obtain between them and another object; nothing could occupy the same place as an object on an earlier occasion. The property of being a "reference object" is included in our definition to reflect the fact that not every alteration in relative position is significant for determining whether two objects occupy the same or different places. For instance, in our previous illustration A, is, on the first occasion, to the left of a C-looking object (C,), but C,, which has replaced A,, is not to the left of a C-looking object (C,). Hence, without the qualification pertaining to reference ob-jects in (61, C, would not be in the same olace that A, was. The selection of a reference group is, to some extent, arbitrary-especially in our artificial examples. Selection of B as a reference object simply means that any alteration in spatial relations between B and any other object shall be taken to constitute a motion, not of B, but of that other object. Calling B a "reference object" reflects the intent, conditioned partly by past experience and partly by present circumstances, of a person viewing the situation to regard it one way rather than another. The intent is conditioned by past experience insofar as a sub-set of the objects being observed have, in the past, maintained highly stable mutual relationships. None of this is capable of being made very precise in ageneral way. Nevertheless, this intent is also conditioned by present circumstances to the extent that the anticipated constancy is maintained. If one of the objects composing the initial reference group (the group which past experience has led us to expect will retain a stable interrelationship throughout the present process) "begins to move" (i.e., alters its spatial relations to the remaining members of the group) the frame of reference is automatically shifted to those remaining objects. Therefore, in treating certain objects as reference objects we have in mind not only the fact that they have, in the past, exhibited stability with respect to each other, but also the fact that they will, on the present occasion, continue to do so--a circumstance that cannot be determined until the motion being described has been completed. The answer to our second objection, then, is as follows: the inclusion of the term
