- Our concept of a physical object's persistence through time seems so fundamental and primitive that it requires a special effort to appreciate what philosophers might be after when they ask for an analysis of this concept. Traditionally the request for such an analysis might take the form of such questions as;
→ What does the identity through time of a physical object consist in?
→ What is it for a physical object which exists at one time to be the same object as a physical object which exists at another time?
In more recent literature one typically finds philosophers asking for an account of our "identity criteria" for objects. This new terminology, at least as I intend to employ it, still expresses very much the same traditional request for an analysis of our identity concept, except perhaps that to talk about "identity criteria" is to signal more clearly one's quite reasonable willingness to settle for an analysis which may be less than airtight and which may allow for many borderline cases1.
- When we ask with regard to physical objects what their identity through time consists in, we are asking for an account of the unity of a physical object's career. Any physical object has a career which stretches over a period of time, a career which we can think of as comprised of a temporal succession of momentary stages. The successive parts, or stages, of an object's career must hang together in some distinctive way; otherwise there would be nothing to prevent us from arbitrarily combining into a single career the early stages of one object with the later stages of a different object. Evidently not just any succession of object-stages corresponds to a single persisting object; some do and some do not. So in order for object-stages to add up to a single persisting object they must be related in some special way. What I am seeking in Part One is an analysis or definition of what that relationship is.
- In a sense, of course, any succession of object-stages, however arbitrary, does add up to something: perhaps to an event, or to a state of affairs or, if nothing else, at least to a "merely arbitrary succession of object-stages." What is important, however, is that not every succession adds up to a persisting object or body (I will use these expressions interchangeably), where this fundamental category is to be understood as loosely comprising items which can straightforwardly be said to occupy space and to persist through time. Clearly only certain privileged successions are accorded the special status of uniting into a single persisting object in this sense, which gives rise to the question as to what the unity-making relationship is in virtue of which some successions enjoy this special status.
- Our question, I want to stress, is primarily conceptual rather than epistemological. We are not, that is, to be thinking primarily of a situation in which someone has not seen an object for some time and a question arises as to how he can know that he has really come across the same object again. Rather we are to be thinking primarily of a situation in which someone continuously observes an object for a stretch of time, and, as I shall often put it, traces the object's career for that period. Our question is what criteria of identity enter into this tracing operation. How can we analyze what it means to judge in those optimal circumstances that it was a single persisting object that was being followed?
- It must be emphasized, furthermore, that this is a question about our most ordinary notion of physical persistence. We want an account of what goes into our thought about the identity through time of tables, trees, and other objects that we ordinarily talk about. A philosopher may of course hold that the ordinary notion of physical persistence is not ultimately important, perhaps because ordinary physical objects are not among the "ultimate constituents of reality." Whatever might be the cogency of this sort of claim (and I shall have something to say about it in the course of what follows), the fact remains that we certainly do have an ordinary way of thinking about the physical world, and it must be of some philosophical interest to provide an analysis of that way of thinking.
- Our question, then, is about as clear as the notion of giving an "analysis" (or a "definition"), which means, I think, that it is not luminously clear at all. One important difficulty with this notion has to do with deciding when an analysis is "circular,'" when, that is, the concepts in terms of which it is couched depend, in some sense, on the concept being analyzed. This difficulty may seem potentially devastating when the concept to be analyzed is as fundamental to our overall thought as the concept of physical persistence. But perhaps we may provisionally adopt a fairly tolerant attitude about this. If we can provide an account of our identity criteria which strikes us as at least not patently circular then we may feel that we have the kind of analytic illumination that we sought. It may turn out, of course, that granted even a reasonable measure of tolerance our concept of physical persistence, or some application of that concept, will seem to resist the sort of analysis that we are seeking. In this case we will have to say that the concept, or some application of it, is, in some important sense, ultimate and unanalyzable. Later, in Chapter 4 ("Hirsch (Eli) - The Persistence of Matter"), I will in fact defend the position that our concept of the persistence of material substance is in a sense unanalyzable. And in Chapter 5 ("Hirsch (Eli) - The Metaphysics of Persistence"), the final chapter of this part, I will consider a bit more forthrightly some of the metaphysical issues that may revolve around the idea of giving an analysis of physical persistence. These issues in their full generality, however, will not be dealt with until Part Two2.
- The topic that I intend to focus upon in this first part is rather severely circumscribed. I want to examine our concept of persistence as it pertains to the seemingly most central and unexceptionable instances of physical objects or bodies. These would include, I assume, such things as tables and cars, mountains and stones, trees and flowers, cats and dogs, chunks of clay and bits of wood. But I shall have nothing to say in this part about the identity conditions for such nonsubstantial items as events and properties, or such corporate items as groups and forests; nor will I enter into the very special problems which seem to affect our concept of the persistence of persons3. Some of these additional issues will be discussed in Part Two.
- An object's unity through time is by no means the only philosophically challenging mode of object-unity. In particular one can raise questions about an object's unity through space which parallel in many ways questions about its unity through time. The spatial question would have to do with our basis for treating some, but not all, aggregates of matter as unitary objects. This question will eventually be addressed in Chapter 3 ("Hirsch (Eli) - The Basic Idea of Persistence"). But in order to focus properly on the immediate question, a question essentially about identity through time, the perspective to adopt is one in which an aggregate of matter has (on whatever basis) already been delineated as a unitary object and our primary concern is to understand what it means to trace that object's career through time.
Footnote 1: On the meaning of "identity criteria" see Footnote 2: See "Hirsch (Eli) - Minds and Bodies: Introduction", and the following Chapters.
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