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.
Reductionism of all sorts has been out of favor for many years. Few among us would now seriously entertain the possibility that ethical expressions are definable, or reducible in some broader sense, in terms of “descriptive” or “naturalistic” expressions. I am not sure how many of us can remember, in vivid enough detail, the question that was once vigorously debated as to whether so-called “physical-object statements” are translatable into statements about the phenomenal aspects of perceptual experience, whether these are conceived as “sense data” or as some manner of “being appeared to”. You may recall the idea that concepts of scientific theories must be reduced, via “operational definitions”, to intersubjectively performable procedures whose results can be ascertained through observation. This sounded good - properly tough-minded and hard-nosed - but it didn' t take long for philosophers and scientists to realize that a restrictive constraint of this sort was neither enforceable nor necessary - not necessary to safeguard science from the threat of metaphysics and pseudo-science. These reductionisms are now nothing but museum pieces.
In philosophy of mind, too, we have gone through many reductionisms; some of these, such as logical behaviorism, have been defunct for many years; others, most notably, the psychoneural identity theory, have been repeatedly declared dead; and still others, such as versions of functionalism, are still hanging on, though with varying degrees of difficulty. Perhaps as a result of the singular lack of success with which our earlier reductionist efforts have been rewarded, a negative image seems to have emerged for reductionisms in general.
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.
EPISTEMOLOGY AS A NORMATIVE INQUIRY
Descartes' epistemological inquiry in the Meditations begins with this question: What propositions are worthy of belief? In the First Meditation Descartes canvasses beliefs of various kinds he had formerly held as true and finds himself forced to conclude that he ought to reject them, that he ought not to accept them as true. We can view Cartesian epistemology as consisting of the following two projects: to identify the criteria by which we ought to regulate acceptance and rejection of beliefs, and to determine what we may be said to know according to those criteria. Descartes' epistemological agenda has been the agenda of Western epistemology to this day. The twin problems of identifying the criteria of justified belief and coming to terms with the skeptical challenge to the possibility of knowledge have defined the central tasks of theory of knowledge since Descartes. This was as true of the empiricists, of Locke and Hume and Mill, as of those who more closely followed Descartes in the rationalist path.
It is no wonder then that modern epistemology has been dominated by a single concept, that of justification, and two fundamental questions involving it: What conditions must a belief meet if we are justified in accepting it as true? and What beliefs are we in fact justified in accepting? Note that the first question does not ask for an “ analysis” or “ meaning” of the term “ justified belief”.
SUPERVENIENCE IN PHILOSOPHY
Supervenience is a philosophical concept in more ways than one. First of all, like such concepts as cause and rationality, it is often used in the formulation of philosophical doctrines and arguments. Thus, we have the claim that ethical predicates are “supervenient predicates”, or that the characteristics of a whole supervene on those of its parts. And arguments have been advanced to show that the supervenience of moral properties undermines moral realism, or that, on the contrary, moral supervenience shows ethical judgments are “objective” after all. And, again like causality and rationality, the concept of supervenience itself has become an object of philosophical analysis and a matter of some controversy.
But unlike causality, supervenience is almost exclusively a philosopher's concept, one not likely to be encountered outside philosophical dissertations and disputations. The notion of cause, on the other hand, is an integral part of our workaday language, a concept without which we could hardly manage in describing our experiences and observations, framing explanationsof natural events, and assessing blame and praise. Something similar can be said about thenotion of being rational as well, although this concept is not as ubiquitous in ordinary discourse as that of cause. Supervenience of course is not unique in being a technical philosophicalconcept; there are many others, such as “haecceity” and “possibleworld” in metaphysics, “analyticity” in the theory of meaning, and the currently prominent concepts of “wide” and “narrow” content.
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.
In his celebrated discussion of causation Hume identified four prima facie constituents in the relation of causation. As everyone knows, they are constant conjunction, contiguity in space and time, temporal priority, and necessary connection. As ordinarily understood, the causal relation is a binary relation relating causes to their effects, and so presumably are the four relations Hume discerns in it. But what do these four relations tell us about the nature of the entities they relate?
Constant conjunction is a relation between generic events, that is, kinds or types of events; constant conjunction makes no clear or nontrivial sense when directly applied to spatiotemporally bounded individual events. On the other hand, it is clear that the relation of temporal priority calls for individual, rather than generic, events as its relata; there appears to be no useful way of construing ‘earlier than’ as a relation between kinds of classes of events in a causal context.
What of the condition of contiguity? This condition has two parts, temporal and spatial. Temporal contiguity makes sense when applied to events; two events are contiguous in time if they temporally overlap. But spatial contiguity makes best sense when applied not to events but to objects, especially material bodies; intuitively at least, we surely understand what it is for two bodies to be in contact or to overlap. For events, however, the very notion of spatial location often becomes fuzzy and indeterminate.
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.
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.
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. […]
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