Donald Davidson's work on the nature of the mind has had a major impact on contemporary discussions in philosophy of mind; it is fair to say that no other philosopher has been more influential in shaping the basic contours of the field as it exists today. As is true in the case of many other philosophers, both of his generation and of following generations, his reflections on mind and its relation to matter have been carried on with a set of broad physicalist assumptions as a backdrop. Precisely what these assumptions are is not easy to say, and it is not necessary to set them down in exact formulations. For most philosophers who have reflected on the status of mind, including Davidson, the main task has been that of finding for mind a place in an essentially physical world. The world is fundamentally a physical world in that the space-time world is the entire world, and that within space-time we find nothing but bits of matter and increasingly complex aggregates made up of bits of matter. As C. Lloyd Morgan, one of the early emergentists, aptly put it, there is “no insertion of alien forces” (Morgan 1923) when complex physical systems are generated out of simpler ones; there are only material elements arranged in new relationships and structures. These material entities have various physical properties – mass, motion, energy, electric charge, temperature, elasticity, and the like – and they behave in accordance with the laws of physics.
Mental Causation and Consciousness
Schopenhauer famously called the mind-body problem a “world-knot,” or “Weltknoten,” and he was surely right. However, the mind-body problem is not really a single problem; it is a cluster of connected problems about the relationship between mind and matter. What these problems are depends, of course, on a broader framework of philosophical and scientific assumptions and presumptions in which the questions are posed and potential solutions are formulated. For the contemporary physicalist, I believe that there are two problems that truly make the mind-body problem a Weltknoten, an intractable and perhaps ultimately insoluble puzzle. These problems concern mental causation and consciousness. The problem of mental causation is to answer this question: How can the mind exert its causal powers in a world that is fundamentally material? The second problem, that of consciousness, is to answer the following question: How can there be such a thing as a mind, or consciousness, in a material world? Moreover, as I will argue, the two problems are interconnected – the two knots are intertwined, and this makes it all the more difficult to unsnarl either of them.
Giving an account of mental causation has been, for the past three decades, one of the main preoccupations of philosophers of mind who are committed to physicalism in one form or another. The problem, of course, is not new: As every student of western philosophy knows, Descartes, who arguably invented the mind-body problem, was confronted forcefully by his contemporaries on this issue. But this does not mean that Descartes's problem is our problem.
It was about half a century ago that the mind–body problem, which like much else in serious metaphysics had been moribund for several decades, was resurrected as a mainstream philosophical problem. The first impetus came from Gilbert Ryle's The Concept of Mind, published in 1948, and Wittgenstein's well-known, if not well-understood, reflections on the nature of mentality and mental language, especially in his Philosophical Investigations which appeared in 1953. The primary concerns of Ryle and Wittgenstein, however, focused on the logic of mental discourse rather than the metaphysical issue of how our mentality is related to our bodily nature. In fact, Ryle and Wittgenstein would have regarded, each for different reasons, the metaphysical problem of the mind–body relation as arising out of deplorable linguistic confusions and not amenable to intelligible discussion. There was C. D. Broad's earlier and much neglected classic, The Mind and Its Place in Nature, which appeared in 1925, but this work, although robustly metaphysical, failed to connect with, and shape, the mind–body debate in the second half of this century. It is fair to say that the mind–body problem as we know it today had its proximate origins in a trio of papers published in the late 1950s: U. T. Place's ‘Is Consciousness a Brain Process?’, in 1956, and J. J. C. Smart's ‘Sensations and Brain Processes’ and Herbert Feigl's ‘The “Mental” and the “Physical”’, published in 1958 and 1959 respectively.
In a series of papers and a recent book, Fred Dretske has been working out an innovative account of how reasons explain behavior. His starting point is what we may call “the causal thesis”, often associated with Davidson, that reasons rationalize behavior by being its cause. With Davidson, therefore, Dretske takes rationalizing explanations to be a species of causal explanation, explanations that specify the causal antecedents of their explananda. Reasons are beliefs, desires, and other assorted “contentbearing” states, and these are among the paradigmatic instances of intentional mental states. Thus, the problem of explaining how reasons rationalize (that is, explain by providing reasons) is, for Dretske, the problem of giving an account of how intentional states can be causes, that is, the problem of intentional or rational causation. If we further assume, with Dretske, that the behavior to be rationalized is, or often involves, bodily events and processes, our problem is seen as a special case of the problem of psychophysical causation, that of understanding how mental events or states can enter into causal relations with physical events, as their causes or their effects. There is of course an even broader problem of mental causation, the problem of explaining how mental events can enter into any sort of causal relation, either as causes or as effects, whether with physical events or with other mental events.
The reality of the mental is closely tied to the possibility of mental causation, and anyone who takes a realist attitude toward the mental must be prepared with an account of how mental causation is possible.
Jonathan Edwards held the doctrine that ordinary material things do not persist through time but are at each moment created, and recreated, by God ex nihilo. He writes:
If the existence of created substance, in each successive moment, be wholly the effect of God's immediate power, in that moment, without any dependence on prior existence, as much as the first creation out of nothing, then what exists at this moment, by this power, is a new effect, and simply and absolutely considered, not the same with any past existence, though it be like it, and follows it according to a certain established method.
Thus, the present “time slice” of this table, although it is very much like the one preceding it, has no causal connection with it; for each slice is a wholly distinct creation by God. The temporal parts of this table are successive effects of an underlying persisting cause, God's creative activity. In arguing for this doctrine, Edwards offers the following striking analogy:
The images of things in a glass, as we keep our eye upon them, seem to remain precisely the same, with a continuing, perfect identity. But it is known to be otherwise. Philosophers well know that these images are constantly renewed, by the impression and reflection of new rays of light; so that the image impressed by the former rays is constantly vanishing, and a new image impressed by new rays every moment, both on the glass and on the eye … And the new images being put on immediately or instantly, do not make them the same, any more than if it were done with the intermission of an hour or a day. […]
Suppose we could create an exact physical replica of a living human being - exactly like him cell for cell, molecule for molecule, atom for atom. Such a replica would be indistinguishable, at least physically, from the original. For we are supposing that the replica is a perfect physical copy in every detail. The idea of such a replica, whether artificially created or naturally found, is a perfectly coherent one; in fact, it is consistent with all known laws of nature. The idea of course is a commonplace in science fiction.
Given that your replica and you are exactly alike physically, will you also share your psychological life with him? Will your replica have your psychological traits and dispositions, intellectual powers and artistic gifts, anxieties and depressions, likes and dislikes, and virtues and vices? Will it feel pain, remorse, joy and elation exactly in the way you do? That is, if two organisms have identical physical features, will they be identical in psychological characteristics as well?
According to many moral theorists, any two things sharing the same ‘naturalistic’ or ‘descriptive’ features cannot differ in respect of moral or evaluative properties. Thus, it has been said that if St. Francis is a good man, anyone who is just like him in all naturalistic respects - in this case, broadly psychological properties, such as traits of character and personality - must of necessity be a good man.
I want to reopen the question whether the same bit of behavior, say an action we perform such as climbing a ladder, can be given both a “mechanistic” explanation, in terms of physiological processes and laws, and a “purposive” explanation, in terms of “reasons” (e.g., goals and beliefs). In a paper published in 1968, Norman Malcolm defended a negative answer. He argued that once an action has been explained by setting forth its physiological causal antecedents it is no longer open to us to explain it by citing the agent's reasons, that is, his beliefs, desires, intentions, and the like. Alvin Goldman immediately replied to Malcolm, arguing that mechanistic and purposive explanations are indeed compatible, that we can in fact characterize a type of situation in which one and the same behavior can be seen to be explainable both physiologically and rationally.
I want to reopen this debate not only because there is more to be said on this issue but also, and more importantly, because the issue has significant implications for some problems of much current interest in the philosophy of mind. A proper appreciation of the broader methodological issues and options involved will, I believe, help us to get clearer about some matters of current controversy. As we shall see, the question of explanatory compatibility leads us to more general questions about the pos-sibility of multiple explanations of a single explanandum, and the relationship between two distinct explanatory theories covering overlapping domains of phenomena.
Asked how badly he wanted to win the Super Bowl Washington Redskin left guard Russ Grimm replied, “I'd run over my mother to win it.” The quote was repeated to Los Angeles Raider inside linebacker Matt Millen, who answered, “I'd run over her, too, - I mean Grimm's mother.”
Accounts of supervenience to date have almost exclusively focused on properties (that is, monadic attributes), although relations are informally mentioned sometimes in connection with supervenience. What happens if relations are explicitly taken into consideration in characterizing supervenience?
Let A be the supervening set of attributes, and B the base set. Consider first the case in which A includes an n-adic relation R, but B includes only monadic properties. It is evident that for R to supervene on B, the following condition is necessary and sufficient:
For any n-tuples, (x1,..., xn) and (y1,..., yn) (to be abbreviated as Xn and Yn respectively), if they are indiscernible in set B, then R(Xn) iff R(Yn)
Depending on whether the n-tuples compared are restricted to a single world or may berecruited from different worlds, this will yield either “weak” or “strong” supervenience (Essay 5). But what is it for two n-tuples,Xn and Yn, to be indiscernible from eachother with respect to B? Since B is assumed to include only properties and norelations, the answer is simple: Xn is indiscernible fromYn in B just in case for each i (1' i' n) xiis indiscernible from yiin respect of B-properties.
The essays selected for this volume have been written over a period of approximately twenty years since the early 1970s, and are reprinted here without changes except for typographical and minor stylistic corrections and the updating of footnotes. Part I consists of papers on the metaphysical issues of events, causation, and supervenience; Part II includes papers on issues in the metaphysics of mind - in particular, mind-body supervenience and mental causation. Each part ends with a set of postscripts indicating my current thoughts on some of the central problems discussed therein.
I wish I could say that I stand by everything I said in these papers; on some issues I do of course, but on others my views have changed, rather significantly in a few instances, and I expect them to continue to change and evolve. On some of the issues I am not even clear just what I am now prepared to defend. This is the case, for example, with the theory of events. In Essays 1 and 3, I formulated and argued for what is now standardly called the “property exemplification” account of events, and I still think that it is a viable approach. However, I am now inclined to think that ontological schemes are by and large optional, and that the main considerations that should govern the choice of an ontology are those of utility, simplicity, elegance, and the like.
It is part of today's conventional wisdom in philosophy of mind that psychological states are “multiply realizable”, and are in fact so realized, in a variety of structures and organisms. We are constantly reminded that any mental state, say pain, is capable of “realization”, “instantiation”, or “implementation” in widely diverse neural-biological structures in humans, felines, reptiles, mollusks, and perhaps other organisms further removed from us. Sometimes we are asked to contemplate the possibility that extraterrestrial creatures with a biochemistry radically different from the earthlings', or even electro-mechanical devices, can “realize the same psychology” that characterizes humans. This claim, to be called hereafter ‘the Multiple Realization Thesis’ (“MR”, for short), is widely accepted by philosophers, especially those who are inclined to favor the functionalist line on mentality. I will not here dispute the truth of MR, although what I will say may prompt a reassessment of the considerations that have led to its nearly universal acceptance.
And there is an influential and virtually uncontested view about the philosophical significance of MR. This is the belief that MR refutes psychophysical reductionism once and for all. In particular, the classic psychoneural identity theory of Feigl and Smart, the so-called “type physicalism”, is standardly thought to have been definitively dispatched by MR to the heap of obsolete philosophical theories of mind. At any rate, it is this claim, that MR proves the physical irreducibility of the mental, that will be the starting point of my discussion.
The term ‘event’ ordinarily implies change, and most changes are changes in a substance. Whether coming into being and passing away can be construed as changes in substances is a question we shall not consider here. A change in a substance occurs when that substance acquires a property it did not previously have, or loses a property it previously had. Whether fissions and fusions of substances can be considered as cases of losing or acquiring properties is, again, a question we shall not discuss in this paper. By ‘substance’ I mean things like tables, chairs, atoms, living creatures, bits of stuff like water and bronze, and the like; there is no need here to associate this notion with a particular philosophical doctrine about substance.
Besides events, we also speak of “states”. If “events” signal changes,“states” seem to be static things, “unchanges”, to use a term of C. J. Ducasse's; some examples of states would be my body's weighing 140 pounds, the earth's being nearly spherical in shape, and the presence of oxygen in this room. There are, however, good reasons for not taking this dichotomy of changes and unchanges, or of events and states, too seriously at the initial stage of developing a theory of events. For one thing, there are cases that are hard to classify e.g., the whirring of my typewriter, having a throbbing pain in the right elbow.
In an earlier paper, “Concepts of Supervenience,” I characterized two distinct concepts of supervenience, “strong” and “weak,” and compared them with each other and with a third concept, “global supervenience.” In this paper I wish to correct an error in the earlier paper and present further material on supervenience, including a new characterization of strong supervenience, which I believe is particularly perspicuous, and a discussion of the adequacy of global supervenience as a determination relation. I shall also present a strengthened relation of global supervenience based on similarity rather than indiscernibility between worlds, which may well be a more useful concept than the currently popular conception of global supervenience.
A NEW CHARACTERIZATION OF “STRONG SUPERVENIENCE”
Let A and B be two sets of properties (closed under complementation, conjunction, disjunction, and perhaps other property-forming operations). A is said to weakly supervene on B just in case:
(I) Necessarily, for any x and y, if x and y share all properties in B, then x and y share all properties in A - that is, indiscernibility in B entails indiscernibility in A.
This corresponds in a straightforward way to the informal characterization of supervenience commonly found in the literature. As was shown in the earlier paper, weak supervenience can be equivalently explained as follows:
(II) Necessarily, for any object x and any property F in A, if x has F, then there exists a property G in B such that x has G, and if any y has G, it has F.
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