Philosophy of Nature and Quantum Reality
Ian J. Thompson Department of Physics University of Surrey 2 Preface
This manuscript is a third draft. Any responses would be gratefully received. Earlier versions of parts of chapters 1, 2, 3 and 8 have appeared in articles in Cogito and The British Journal for the Philosophy of Science. For comments and criticism at various stages in the development of this book, I would like to thank John Mayberry, Dorothy Emmet and Nicholas Maxwell. I am grateful to Peter Alexander, Michael Welbourne, David Hirschmann, Adam Morton and Edo Pivcevic for reading and listening to several related papers during my stay at Bristol. I would especially like to thank my wife Judy for the time and space to accomplish this work. I.J. Thompson, Bristol 1988, revised Surrey 1993 Draft Only c Ian J. Thompson 1988, 1993 A Layout with L TEX 3 4 Contents
1 2 Prospects for a Philosophy of Nature Dispositions 2.1 Everyday Dispositions . . . . . . . . . . . . . . . . . . . . . 2.2 Derivative Dispositions . . . . . . . . . . . . . . . . . . . . . 2.3 Are Dispositions Real? . . . . . . . . . . . . . . . . . . . . . 2.4 Scientific Explanation of Dispositions . . . . . . . . . . . . 2.5 Are Bases ultimately Dispositional, or Non-dispositional? . 2.6 Objections to Dispositional Bases . . . . . . . . . . . . . . . Problems in Classical Physics 3.1 Newtonian Physics . . . . . . . . . . . 3.2 Descartes and Leibniz . . . . . . . . . 3.3 Aristotle's Physics . . . . . . . . . . . . 3.4 Dispositions in Mathematical Physics The Peculiarities of Quantum Physics 4.1 Classical and Quantum Dispositions 4.2 Quantum Experiments . . . . . . . . 4.3 Quantum Ontologies . . . . . . . . . 4.4 The Problem of Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 13 13 16 18 20 21 22 27 28 29 30 31 35 35 35 36 40 43 47 47 49 56 61 61 65 67 71 71 73 3 4 5 6 Reconsidering Philosophical Foundations Actuality 6.1 On What Can Be Actual . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2 Finite or Infinite? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3 Choices for Pure Actuality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Potentiality 7.1 Change as Actualising . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2 The Analysis of Actualising (Kinesis) . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3 Kinds of Potentialities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A Theory of Space and Time 8.1 Possibilities as Places in Space and Time . . . . . . . . . . . . . . . . . . . . . . . . 8.2 Extensiveness, Space and Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 7 8 6 8.3 8.4 8.5 8.6 9 Past and Future . . . . . . . . . . . . Process Time . . . . . . . . . . . . . . One Global Process Time? . . . . . . Necessary and Contingent Ordering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CONTENTS
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 80 83 87 91 91 92 94 95 96 96 96 97 99 100 100 101 101 101 103 107 109 111 111 114 116 123 125 125 127 127 130 132 134 136 A Theory of Substance 9.1 Traditional Views of Substances . . . . . . . . . . . . . . . . 9.2 Propensity Fields . . . . . . . . . . . . . . . . . . . . . . . . 9.3 Continuants (Substances) Which Endure Through Change? 9.3.1 Unchanging Continuants . . . . . . . . . . . . . . . 9.3.2 Changeable Continuants . . . . . . . . . . . . . . . . 9.4 Questions about Substances . . . . . . . . . . . . . . . . . . 9.4.1 Individuals . . . . . . . . . . . . . . . . . . . . . . . 9.4.2 Matter and Form: Subject and Predicate . . . . . . . 9.4.3 On Real Essences . . . . . . . . . . . . . . . . . . . . 9.4.4 Elements . . . . . . . . . . . . . . . . . . . . . . . . . 9.4.5 On Time and Change . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Quantum Substances 10.1 Classical and Quantum Theories . . . . 10.2 Probabilities and Propensities . . . . . . 10.3 Waves, Particles and Complementarity . 10.4 Measuring as Actualising . . . . . . . . 10.5 Nonlocalities . . . . . . . . . . . . . . . . 11 Two Stages of Propensities 11.1 Point Events . . . . . . . . . . . . . . 11.2 Actual and Virtual Events as Distinct 11.3 `Gauge' Invariances . . . . . . . . . . 11.4 Quantum Substances . . . . . . . . . . . . . . . . . 12 Measurements and Other Actualisations 12.1 The Problem of Measurement . . . . . . . . . . . 12.2 Objective Actualisation - some proposals . . . . 12.2.1 Simple schemes . . . . . . . . . . . . . . . 12.2.2 Schematic Proposals . . . . . . . . . . . . 12.2.3 Quantitative Proposals . . . . . . . . . . . 12.3 Mind-dependent Actualisation - some proposals 12.4 Conclusions . . . . . . . . . . . . . . . . . . . . . A Summary of the Argument 137 A.1 General Process Logic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137 A.2 When actualities at points in ordinary space and time . . . . . . . . . . . . . . . . 138 A.3 When actualities are selections of alternatives . . . . . . . . . . . . . . . . . . . . . 138 Chapter 1 Prospects for a Philosophy of Nature
In the Twentieth Century, despite the advances of modern science, we are no longer sure what the world is made of. We are confident that it is made out of parts of various kinds, but it has become mysterious what these parts are made of. If we ask the question, `what is it to be a substance?', we might first turn to scientists for an answer, to physicists in particular. A physicist will explain how all kinds of ordinary matter are composed of small atoms, which are composed of electrons, protons, and neutrons. Protons and neutrons are again composed of quarks, he says he believes, but when pressed as to what really are electrons and quarks, he says that he can tell you how they behave, but that he doesn't really know what they are. If he is feeling unkind, he might say `that is a meaningless question', otherwise he will say that the electrons and quarks seem to be some kind of `ultimate particles' whose existence and behaviour you just have to take on trust. `You have to start somewhere', he might add. But when we asked the initial question, `what is it to be a substance?', in a sense we were going straight to the question of these `ultimate particles'. We want to know what the world is really made of, and what are the ultimate individuals in the physical world. We have a feeling that we can't go on looking for smaller and smaller constituents ad infinitum. The process of subdivision should ultimately come to a stop with the `real individuals' that are the real substances of the world. We don't know for certain if physics has yet reached the stage of looking at these ultimate substances. Of course, physicists almost always believe they have come to that stage, but that might just be because they haven't yet done the right kind of experiment. This means that if we want to know what these ultimate substances might be like, we have to turn to philosophy rather than to physics. We will then have to be satisfied with general principles rather than particular knowledge, because philosophers can only argue from general considerations about what is possible, and do not provide detailed knowledge about what actually occurs in particular circumstances. You may think that consideration of `mere possibilities' will not be fruitful, but you would be forgetting that every scientific theory presupposes some general framework about what is possible. Different scientific theories go along with different philosophical frameworks about what our ultimate substances might be like. The physical theories of the Greeks, of Newton and of modern quantum physics assume different philosophical ideas about substances, and these ideas are not compatible with each other. They cannot all be correct! My purpose in this book is to illuminate these different basic ideas, and to see whether there is one set of ideas which recommend themselves as reasonable, and which 7 8 CHAPTER 1. PROSPECTS FOR A PHILOSOPHY OF NATURE can help us understand the world and its peculiarities as revealed by quantum physics. Accommodating Quantum Physics
It is largely because of the difficulties in understanding modern quantum physics that many people have realised to need to re-examine the foundations of physics. As a result of quantum mechanics, questions have been continually raised concerning some of the deepest questions in philosophy, such as whether the world exists independently of our observations or of our minds, whether physical substances exist and/or have any definite properties, whether these properties (should they exist) are in any way knowable, and whether indeed anything could be said to have definitely happened to the exclusion of its alternatives. Many, in a kind of agnosticism, have despaired of positive answers to these questions ever being found 1 , and others have turned to philosophies where it is accepted that `objective reality' is altogether an ephemeral by-product, or an illusion of some kind 2 . When, therefore, we do reconsider foundations, we are almost overwhelmed by the enormous range of physical theories and natural worlds that are logically possible. Reece [1973], Jammer [1974] and Herbert [1985] survey some (but not all!) of this range. Rather than being lost in the maze of science-fiction-like realms, a better approach would be to think more carefully about the collection of general ideas which we bring to bear when we look at nature. Traditionally, these have been the four "ultimate" concepts used to characterise nature: matter, motion, time and space. Leibniz was the first to point out the inadequacies in these four "ultimates", and how the first (`matter') was not essentially related to the other three. (We will be looking in more detail at these notions of classical physics in chapter 3.) His was merely the beginning of a long line of critiques of the ideas of physics, pointing out that the basic concepts of many theories are not properly consistent with each other. It is of course possible to argue `that even the ideals of clarity and consistency can be legitimately compromised in order to obtain other advantages' (Edwards [1985]), but this can at best be only a temporary manoeuvre. It is only after careful consideration of the ultimate concepts we use, and the finding of a consistent set, that we can have any confidence in them as realistic descriptions of nature. The kind of discussions here can best be called the philosophy of nature. This term is not in popular use, but it is needed in order to distinguish our endeavours from the philosophy of science, and from the philosophy of knowledge. In the philosophy of nature we are going to consider ontological problems directly, and not let them be obscured by questions of methodology and epistemology. That is, we are going to pose and answer questions about what exists, and not be side-tracked into questions of `how can we be sure of that?', or of `how should we discover what exists in this test-tube?'. In doing this, we want to take a realistic view of our theories, at least, that is, when they have been considered carefully and found consistent and adequate. We are not taking a merely `instrumentalist' view of theories, whereby their only use is to enable correct predictions. Nor are we taking a merely `phenomenological' view of theories, whereby their only use is to describe our observations and experimental results as does a map. Of course, if a theory is realistic and correct, it will enable both correct predictions and accurate descriptions: these tasks are non-trivial and are still important! We may picture our theories as maps of reality. If our maps of reality were comprehensive and consistent with each other, there would be little demand for further investigations in the
e.g. Heisenberg (following Kant) declares that `things in themselves', while presumably existing, will be forever beyond the range of human knowledge. 2 e.g. from Schrodinger [1958] to Capra [1975], Toben [1975] and Zukav[1980]. �
1 9 philosophy of nature. The problem, in modern times, is precisely that our maps are fragmented, confused, and often appear to contradict each other. Physicists survive in this situation by marking various regions with large `Keep Out' signs, and learning to choose which of their opposing maps should be used in the various stages of their travels. Richard Feynman [1967], for example, writes I think it is safe to say that no one understands quantum mechanics. . . . Do not keep saying to yourself, if you can possibly avoid it, `But how can it be like that?' because you will get `down the drain' into a blind alley from which nobody has yet escaped. Nobody knows how it can be like that. These practices and warnings seem more akin, however, to that of the medieval cartographers when they wrote `here be dragons'. Feynman may well have a point about the difficulties and dangers in trying to answer the question `What can the world be like such that quantum mechanics can be true of it?', but what we need therefore are suitable new instruments of analysis which are precise and versatile. We will need to extend many of our common sense ideas beyond their original scope, while at the same time always considering carefully exactly how they can still be applied. The Philosophy of Nature
The method adopted in this book is explicitly hypothetical and deductive, rather than being an analysis either of our phenomenal experiences, or of contemporary scientific theories. I will hypothesise the existence of various things (`actual particulars' and `propensity fields', as they will be called), and then the consequences of these will be drawn out in a deductive fashion. In any hypothesising, however, I do not proceed randomly. Both the direction and aims of much of this book are strongly influenced by Ivor Leclerc's excellent investigations (Leclerc [1972], [1986]) of the many past accounts in the philosophy of nature that have been put forward in the history of Western philosophy. He has been useful in providing critical reassessments of the fundamental issues involved in our realistic understanding of the nature of the physical world. His historical perspectives are as valuable as his re-examination of the root problems which have recurred almost unfailingly through the history of the philosophy of nature. The most common problems are those of clarifying, distinguishing and then relating the categories of � actual vs. potential vs. possible, � infinite vs. finite, � continuity vs. discreteness, � becoming vs. being, � substance vs. form vs. act, and � simple vs. compound. It is from suggestions in his work that I derived my initial hypotheses concerning actualities and potentialities. What I am now trying to do is to present these concepts and their relations in a coherent whole. I will be analysing in more detail the categories of actuality and potentiality, 10 CHAPTER 1. PROSPECTS FOR A PHILOSOPHY OF NATURE and hope to flesh out the resulting categorical framework so that it has consequences of any detailed science of nature. The category of dispositions and potentialities is the single most important category that must be considered anew. Science has always had a kind of love-hate relation with properties in this category, accepting their necessity and usefulness, but refusing to live happily with them. In general, it is modal properties of all kinds that cause problems. These properties deal with what might happen, and, despite their apparent remoteness and seeming unreality, we will see in the next few chapters that they have an essential role in all kinds of scientific investigations. Although various ideas of potentialities and propensities have been proposed to help solve difficulties in physics, they have been criticised as being too vague. Hooker 3, for example, remarks that this "approach to quantum theory must inevitably prove less than satisfying. Any theory whatever, so far as I can see, could have its problems `solved' by this approach -- simply because the concept of an `actualisation' of a `potential' is so vague and intrinsically not open to direct investigation of its structure." My aim in this book is therefore to see how potentialities etc. can be understood sufficiently precisely, and then how potentialities and dispositions can be fitted into a broad realistic view of the world. It may be objected that I really seem to be doing speculative physics all along (or, that if not, I ought to be), but that would be to misunderstand the relation between science and the philosophy of nature. It has been remarked that quantum physics is not itself a physical theory, since it does not specify any particular laws for potentials: rather, it is a methodological and mathematical framework in which one can formulate physical theories. Similarly, the philosophy of nature is not itself a scientific theory (either methodologically or mathematically), but rather a framework in which quantum theories can be formulated and interpreted realistically. The task of the philosophy of nature is to provide a general scheme for what can reasonably be said both to exist and to be subject to change. Quantum theories then select some specific scheme, with particular laws of change in specific kinds of spaces. As a consequence of quantum physics it has often been said that we have to give up any hope of a pictorial, literal or realistic description of what goes on in the micro-world of atomic phenomena. We seem at best to have only metaphorical and/or mathematical descriptions, without any clear idea of the reality to which they refer. Sometimes we are told 4 that certain ideas (e.g. those of classical physics), while necessary for all our knowledge, are in fact false. At other times, it is contended that "quantum physics conflicts with the ontological form of thought"5 . I will be arguing, instead, that the lack of literal and realistic ideas betrays more a lack of imagination than a lack in reality. It ought to be possible to interpret some ideas realistically, as being unequivocally and literally true -- once (of course) we have ideas which are good enough. We ought to be able to find ideas that we can interpret literally, and not be forced forever to resort to ideas based merely on mathematical formalisms or metaphors. One important aim is to formulate a description of the world of relativity and quantum physics that is independent of classical physics, so that we can bypass some of the unwanted legacies which have accumulated from the theories of material corpuscles. The task of this book is to produce a formulation in sufficient detail that an understanding of quantum physics begins to be possible. Even though the present investigations will not produce a complete
Hooker [1973], p. 204. e.g. Bohr and the Copenhagen interpretation of quantum mechanics. They want to see quantum mechanics as "a rational generalisation of the classical mode of description" necessitated by the existence of the quantum of action (see Petersen [1968]). 5 Petersen [1968], p. 128.
4 3 11 physical theory, I hope to show that they are still valuable in providing some general ideas which are reasonable, which can be realistically interpreted, and which contribute in some part to our understanding of the world we live in and its quantum peculiarities. 12 CHAPTER 1. PROSPECTS FOR A PHILOSOPHY OF NATURE Chapter 2 Dispositions
2.1 Everyday Dispositions
Nearly everything we do from day to day is influenced by dispositions and knowledge of dispositions. The concept of `dispositions' is central to this whole book, and as I will be arguing that they are the neglected and misunderstood key to any realistic understanding of nature, I will take some time to explain their meaning. To say that salt is soluble in water, that this piece of metal is flexible, that glass is fragile, or that steel is hard, is to ascribe dispositional properties to these things. These are the kinds of things that can be determined by experimental investigations, and are general facts for which we can collect evidence. Often a single trial will be sufficient to determine, say, that salt does dissolve in water when suitably immersed. The meaning of saying that salt is soluble, we should note, goes beyond reporting the results of our few experiments. It is to say that it is a general property of salt that whenever it is placed in water, then it will dissolve. Similarly, to say that this piece of metal is flexible, is to say that whenever it is subject to a transverse pressure, then it will bend. To say that steel is hard is to say that whenever it is subject to a force, then it will be only slightly deformed. To say that glass is fragile is to say that whenever it is suitably hit it will break. What is important about dispositional properties is this `if . . . then . . .' feature. Dispositions are thus different from other properties such as place, size and shape which describe only present states of affairs, and make no reference to what might happen in the future. For this and other reasons, there has been considerable debate within the philosophy of science as to the extent and importance of dispositional properties, against what we might call purely static or structural properties. The issue of dispositional versus static properties will be considered latter in the chapter, for it is important, as Mackie [1973] points out, to separate three different sorts of question: questions about meaning, about what is being said when dispositions are ascribed to things; questions about what we know, about when and how we are able to ascribe dispositions to things; and questions about what is there, about what sorts of properties or states or processes are objectively present in the things that we describe in dispositional terms. To these, I add questions of reality, whether we can completely avoid dispositional terms, and questions of explanation, as to how dispositional properties are in fact explained scientifically. A great many terms have been used over the years to describe what we call here `dispositions' or `dispositional properties'. In a very general sense, any `ability', `capability' or 13 14 CHAPTER 2. DISPOSITIONS `capacity' refers to a meaning of this sort, but as these words have meanings far beyond the philosophy of nature, we will not adopt them as technical terms. Aristotle used the term dynamis (potentiality) to refer to the general capability of things to cause changes in others. Locke [1706] used the term `power', and says that fire has a power to melt gold, and gold has a power to be melted; that the sun has a power to blanch wax, and wax a power to be blanched by the sun. We are abundantly furnished with the idea of `passive power', he points out, by almost all sorts of sensible things. More recently, Harr� 1 has revived the word `power' as a general e term for scientific explanations, and his powers are either identical with dispositions or closely related to them. In science, terms such as `force' and `potential' (as in `potential energy' or `field potential') have been introduced, and these are all dispositional in an essential manner. I will be using the terms `power', `potential', `capability', `capacity', `propensity' and `cause' all as examples within the class or category of `dispositional properties of objects'. (There will be more discussion of these different terms in chapter 7.) Propensities: Probabilistic Dispositions
Not all dispositions are what Mackie [1973] calls `sure-fire' dispositions. Those are the dispositions, like the solubility of salt and the hardness of steel, which are always manifested if the disposition is still in fact present. Other dispositions may manifest themselves only probabilistically. The disposition of a radioactive nucleus to decay, for example, does not manifest itself as a definite event immediately after the nucleus was formed: that is just when the decay first becomes possible. Instead, the disposition to decay appears as a certain propability to decay in any time interval. And furthermore, this propability may vary with time even while (i.e. before) it is not being manifested. After Popper [1959], we use the term propensity to refer to dispositions with any kind of probabilistic outcome. They will clearly come in handy when we want to describe quantum mechanics. Propensities are properties of objects which, in appropriate circumstances, give rise to real and objective probabilities. These probabilities, if they are truly the product of propensities, are not merely an expression of ignorance or partial knowledge on our part. We sometimes still consider dice to have propensities for landing with different numbers upward. As this is only because of our ignorance of their exact trajectories, however, they only have `propensities' in a secondary or `subjective' sense2. Exactly whether and how there can be any real and objective propensities will be discussed below, in the context of that question for dispositions in general. Kyberg [1974] and Maxwell [1976] have more specific discussions of the probabilistic aspects, and give detailed comparisons with the frequency interpretation of probabilities. Humphreys [1985] discusses the question of whether talk of propensities can be replaced by talk of probabilities. Questions of Meaning
If we want to know what it means when we say that salt is soluble, we will need to know that the `if . . . then . . .' phrase means. We need to specify both the antecedent condition, the manifesting occurrence, and the logic of the `if . . . then . . .' expression. In general, the ascription of properties in dispositional category is of the form
see e.g. Harr� [1970a] and Harr� & Madden [1975]. e e Unfortunately Popper [1959] confuses these two `objective' and `subjective' senses of propensities. His work needs other clarifications and corrections too: see for example Gibbins [1987], pp. 79 - 82.
2 1 2.1. EVERYDAY DISPOSITIONS
Object S has the disposition P to do action A if S is in some circumstance C, C depending on P and the character of A, then there will be a non-zero likelihood of S doing A. 15 Here, the `action A' can either be a change in S itself or an interaction with other objects. The suitable `circumstance C' is usually defined by multiple spatial relations to other objects, and will be different for different dispositions for different actions. The circumstance C is said to depend only on the `character' of the action, and not the action itself, because possibly, if the disposition is never manifested, there may exist no such action, at any time in the past, present or future. The circumstance C should depend only of the kind of event expected, and not on its actual occurrence. Finally, the phrase `non-zero likelihood' is designed to be sufficiently general to allow both sure-fire dispositions and probabilistic propensities. It has the consequence that if the probability of an event (while varying with time) touches zero, then there is no propensity at that particular time, but this is surely a reasonable feature. Harr� and Madden [1975] add a phrase `in virtue of the constitution of S' to the above form, e in order to exclude `changes' to certain properties of S that are changes in purely external relations that may come about completely independently of whatever S is actually like. Thus, for example, no disposition of Socrates is necessary to explain his becoming smaller than Theaetetus, if it is the latter who is growing. Mackie [1973] argues however, that it is not part of the logical meaning of a disposition that it is based on some internal form of the objects concerned. He admits that the existence of some basis is an extremely plausible empirical hypothesis, but not that it is logically implied by every ascription of a disposition on all occasions. This question of `basis' will be further discussed below. As is well known, the logical meaning of the `if . . . then . . .' expression italicised in the above form of ascription can not be taken to simply be the material conditional. The meaning of `x is fragile' -- F(x) -- cannot be defined as F (x) = (t) H(x, t) B(x, t) (2.1) where H(x,t) means `x is hit at time t' and B(x,t) means `x breaks at time t', because this would make fragile every object that was never hit. If we defined F(x,t) to mean x is fragile at time t', then F (x, t) = H(x, t) B(x, t) (2.2) would make fragile at t every object that was not hit at time t. Mackie [1973] describes a variety of alternative logical expressions designed to capture the required if/then meaning, and how their inadequacies indicate that we need conditionals which are not themselves purely material conditionals. Neither, he and Mellor point out, can dispositional statements involve purely counterfactual conditionals, as then we get the absurd result that salt is no longer soluble once it is dissolved. D'Espagnat [1979] explains how one could try to use what Carnap called `partial definitions' for the meaning of dispositional terms. This amounts to translating the statement `x is fragile at time t' into a `reduction sentence' of the type If x is hit at time t, then it is called fragile if and only if it breaks. or, in the language of predicate calculus, H(x, t) (F (x, t) B(x, t)). (2.3) 16 CHAPTER 2. DISPOSITIONS This definition can be verified not to suffer from the deficiences of the previous proposals. On the other hand, d'Espagnat points out, the range of definition (2.3) is obviously much smaller than that of definition (2.2). This is because (2.3) yields no interpretation for a statement such as `object x is fragile and it is not being hit'. If no other partial definitions of `fragility' are then applicable, the statement turns out, to the logician, to remain incomprehensible and even meaningless. The conclusion both Mackie and d'Espagnat come to is that dispositional statements are equivalent to some kind of non-material conditional outside the range of traditional (nonmodal) formal logic. They cannot, furthermore, be identified specifically with counterfactual conditionals. The if . . . then in F (x, t) = if H(x, t) then B(x, t) is therefore non-material: whether the statement would take an open, subjunctive or counterfactual form depends on the circumstances and on the speaker's beliefs about the circumstances. If the glass was known not to be hit at time t, then a counterfactual form is appropriate; if it was known to be hit at time t, then we have simply F(x,t) B(x,t); whereas if it is not known whether it was hit or not, then we use the subjunctive form `if the glass were to be hit, then it would break'. These implications together amount to what Mackie calls a minimal disposition. The ascription of a minimal disposition is taken as equivalent to the assertion of a suitable non-material conditional, and this encompasses a large part of the everyday meaning of dispositional properties. They allow dispositions to be ascribed both when they are being manifested and when they are not. They allow glass to be fragile for a while, and then to be toughened by heattreatment and to be fragile no longer. They allow a piece of wrought iron to have a period of brittleness when it was cooled to then temperature of liquid air. They also allow a thing to have a disposition even if neither it or anything else ever manifests that disposition (such as the disposition for a nuclear explosion, to use an example from Mellor [1974]). 2.2 Derivative Dispositions
Before examining in more detail the general features of dispositions, I want time to explain the general idea of a `derivative disposition'. I first show by examples what is meant by the term, and then examine how such dispositions differ from `component dispositions'. This means that they are not part of the prior disposition, but that they are generated by action of the prior disposition in suitable circumstances. Derivative dispositions are not very common in physical theories, the best example being perhaps that of potential energy. Energy itself is kind of disposition to interact in a certain way, so potential energy -- defined usually as `the ability to do work' -- is thus the disposition to produce dispositions with specific values of kinetic energy. The potential energy in a coiled spring, for example, is thus the disposition to move the spring with certain velocities (kinetic energies), and these movements of the spring are dispositions to interact in certain ways with whatever is in its path. Many more interesting examples of derivative dispositions can be found in everyday life. They arise whenever the accomplishment of a given disposition requires the operation of successive steps of kinds different from the overall step. The original disposition on its operation therefore generates from itself the `derived dispositions' for the intermediate steps, which are 2.2. DERIVATIVE DISPOSITIONS 17 means to the original end. An original `disposition to learn', for example, can generate the derived `disposition to read books', which can generate further `dispositions to search for books'. These dispositions would then generate dispositions to move one's body, which in turn lead ultimately to one's limbs having (physical) dispositions to move. These successively generated dispositions are all derived from the original disposition to learn, according to the specific situations. One example of original and derivative dispositions is the ability to learn. To say that someone is easy to teach, or that they are musical, for example, does not mean that there is any specific action that they are capable of doing. Rather, it means that they well disposed to learn new skills (whether of a musical or of a general kind), and that it is these new skills that lead to specific actions. Another example is of three `degrees' of derivative dispositions. Swedenborg [1763] proposes that `conatus', force and motion form a series of `discrete degrees' in living things, with force being derivative from conatus, and motion from force. It is known that conatus does nothing of itself, but acts through forces corresponding to it, thereby producing motion; consequently that conatus is the all in forces, and through forces is the all in motion; and since motion is the outmost degree of conatus, through motion conatus exerts its power. Conatus, force and motion are no otherwise conjoined than according to degrees of height, conjunction of which is not by continuity, for they are discrete, but by correspondences. For conatus is not force, nor is force motion, but force is produced by conatus, because force is conatus made active, and through force motion is produced; consequently there is no power in conatus alone, nor in force alone, but in motion, which is their product. That this is so may still seem doubtful, because not illustrated by applications to sensible and perceptible things in nature: nevertheless, such is the progression of conatus, force and motion into power3. Talk of derivative dispositions is taking the view, following Swedenborg and more recently Broad [1925], that there are `levels' of causal influence here. It allows that particular dispositions or intentions are best regarded not as the most fundamental causes, but as `intermediate stages' in the operation of more persistent `desires' and `motivations'. The intention to find a book, for example, could be the product or derivative of some more persistent `desire for reading', and need only be produced in the appropriate circumstances. Broad would say that the derived dispositions were the realisation of the underlying dispositions. In each particular case, there is clearly scope for many specific and detailed investigations. The point is that whatever the details may be, the `process logic' to be developed in this book can be applied at each level or stage. This is because the process logic can be applied both to the production of actual events, and also to the production of further `derivative dispositions' at a `second stage'. That such derivative dispositions can be formed means the original disposition was not a simple disposition, but had some complexity in its first appearance. However, the `disposition to search for a book' is not strictly a component of a `disposition to learn', in the sense of being always an actual part of that disposition, as it is only derived in appropriate circumstances. For this reason we talk of `derived' rather than `component' dispositions, as the `disposition to learn' is not simply the mere aggregate of all the dispositions that can be derived from it,
3 Swedenborg [1763], �218. 18 CHAPTER 2. DISPOSITIONS just as any disposition or cause is not merely an aggregate of all its possible effects. Rather, the original disposition is more like a `higher order' disposition to generate its derived dispositions according to circumstances. Just as the effects of a disposition are not contained within it, but are generated from it according to circumstances, so derived dispositions are not contained within a higher-order disposition, but are generated from it according to circumstances. The notion of `derivative dispositions' will be used again in chapter 11. 2.3 Are Dispositions Real?
It seems that dispositions are real properties of the things which have them. Before going on to look at the scientific explanation of dispositions, I want to consider some possible philosophical reasons for doubting the reality of dispositions. We might find force, for example, in one or more of the following objections: (a) that one should deny the subjunctive in the power ascription as anything more than hypothetical, (b) science should be content with finding only the regularity of effects, and not try to discover causes and determining constitutions, (c) that causes are only (previous) events and not powers & dispositions, or (d) that the world should be considered as a `Zeno universe' that has only successive states and no proper changes. Taking approach (a), Ryle ([1949], ch. 5) denies that dispositional ascriptions `assert extra matters of fact' and claims that they are only `inference-tickets, the minimal dispositions which licence us to predict, retrodict, etc.' That is, he would omit any `in virtue of the constitution of S' phrase in the meaning of dispositions, and, in a sense, make dispositions strange kind of things `no more substantial than a promise' (as Herbert [1985] puts it). Since then, there is no property of S which makes the ascription true, that truth cannot be explained by properties of S. Thus Ryle (quite explicitly) denies that one should even look for either causal or mechanistic explanations of the dispositions. Even, presumably, in cases in physics and chemistry where there are quite obviously explanations in terms of constituents and their propensities to attract and repel each other. His restriction on looking for explanations in terms of internal dynamics is largely disregarded in scientific practice. Concerning injunction (b), I accept that all observations are of effects rather than of causes, but that does not mean we cannot conceive of causes and of the way they might lead to effects. It seems to me quite legitimate for causes to be postulated in a Popperian fashion, and the consequences deduced for the production of effects. The reverse induction is quite different : obviously we cannot deduce precise causes from observable effects (as Hume has long pointed out), but that does not mean that there no causes. It should not be necessary to accept Hume's [1739] conclusion that "the distinction, which we often make between a power and the exercise of it, is without foundation". The attitude of (c) has been taken by Davidson [1967], when he argues that causality is a two-place relation between individual events. Thus causal relations are certainly not just implications from the description of the first event to that of the second event, but are something more real. The reality of causality, however, does not thereby automatically include such components as dispositions and propensities, although Steiner [1986] wants to extend Davidson's ideas in this direction. I want to allow both dispositions and previous events to be causes, although in different senses. A distinction thus ought to be made between the `Principal Cause' (that disposition which operates), and the `Instrumental Cause' (that circumstance by means of which dispositions operate). Principal causes operate according to instrumental causes. Both are necessary for any 2.3. ARE DISPOSITIONS REAL? 19 event, for example, when a stone is let fall: the principal cause is the earth's gravitational attraction, and the instrumental cause is our action of letting go. Its hitting the ground is thus caused by our letting go, but only as an instrumental cause. Many common uses of `cause' (including that of Davidson [1967]) refer to instrumental causes rather than principal causes, as it is only in the instrumental sense that events can be said to be causes. Previous events cannot be efficacious causes, Emmet [1984] points out, in the sense of `producing' or `giving rise to' their effects. Davidson would argue that that the `onslaught' (i.e. the beginning) of a state or disposition is an event: `a desire to hurt your feelings may spring up at the moment you anger me; I may start wanting to eat a melon just when I see one.' 4 That commencement event could then be regarded as the event which is the cause of the effects of the dispositions and desires. The difficulty with this argument is that only some, but not all, dispositions have initiating events of this kind. It is difficult, for example, to pinpoint the events which initiated the gravitational disposition of the earth, and the solubility of salt. In these instances, as elsewhere, it makes more sense to give a (principal) causal capacity to the dispositions themselves. To consider (d) the world as a `block universe' or `Zeno universe', as recently pointed out by Emmet [1984], is to see only different states of affairs at successive times, and not to see the changes that lead to these differences. Since the rise of Einsteinian relativity, it has become popular to see all of time and space in one `block continuum' of four dimensions, and to see change as only the difference between successive `time slices' of this continuum. In this world there is only what actually happens, and as in (a) above, what `might have happened' is purely hypothetical. The only sense of `might happen' that can be invoked is to imagine an entirely new possible world, e.g. one with different initial conditions or different physical laws. This world view thus does not base power ascriptions on any real features of this particular universe. If we reject the `block universe' account of time, we are also rejecting the view of time in which the future is `already formed' and perfectly definite in advance of its happening, if indeed on this account anything happens at all. (In extreme versions of this theory, time and real change are both completely illusory, but Grunbaum � ([1973], ch. 10) shows that more moderate positions can be held.) I admit that these accounts have an internal consistency that makes them difficult to refute, but despite their being advocated by many philosophers and physicists since Minkowski, I do not believe that they should be the only coherent metaphysical systems on offer. In chapter 8 it will be seen that alternatives can be devised that not only have more explanatory power (e.g. for quantum physics, as in chapter 10), but also more practical use (see below, end of this section). Once these alternatives have been formulated, we should be able to judge in which way our world is most adequately described. Rejecting the objection (d), however, does not mean rejecting all talk of the spacetime continuum. One alternative approach (following Maxwell [1968, 1985 �5 & 6]) says that it is facts about objects, rather than objects themselves, that are (or can construed to be) spread out in time. Spatial relations are between objects, but temporal relations are between facts about objects. Another view follows Whitehead in regarding the spacetime continuum as giving the ordering of possible events (even before there are any actual events). This prospect will be further examined in chapter 8.
4 Davidson [1963], p. 694. 20 CHAPTER 2. DISPOSITIONS It does in any case seem very odd to deny that objects have dispositional properties that relate what might happen as well as what actually happens. To deny causes apart from their manifestations, Mellor [1974 p. 173] shows, leads to some bizarre consequences, for then a disposition could not be ascribed when its operation is impossible. Taking precautions to avoid the conditions in which nuclear fuel would explode, to use his example, should not mean that the fuel was not explosive. `It is ridiculous to say that their success robs the fuel of its explosive disposition and thus the precautions of their point.' Furthermore, a theory that only predicted what actually happens, and not what might happen, would be useless as an engineering planning tool. For it would not be able to predict the consequences of a plan that we might consider employing, but in the end did not actually use. Such a theory could not tell us, for example, what would have happened if one of the unsuccessful channel-tunnel designs had been chosen. These questions are of great practical (and political) importance, and, as we shall see in the next chapter, real physical theories are of course most useful here. 2.4 Scientific Explanation of Dispositions
Usually we expect more of dispositions than the mere holding of a conditional relating a circumstance to a result. We expect that the disposition has some scientific explanation in terms of some other properties of the object involved. The holding of a `minimal disposition', we think, points to some deeper explanation in terms of the causal features of the object and/or its parts. Science, it seems, cannot simply accept an explanation of an object breaking in terms of just its `fragility', of an plant seeking light in terms of just its `phototropism', or the sleep-inducing powers of opium in terms of merely its `dormative virtue'. Dispositions are very often regarded by the scientist as merely a sign that he has to work harder, to find the underlying structures and their causal relations. This process of finding explanations of observed dispositions in terms of constituents has been spectacularly successful in an enormous range of cases (but not all, as we shall see). The solubility of salt is explained by the facts that salt is made of two ions Na + and Cl- , and that these constituents interact in such a way with the H 2 O molecules in liquid water that they become separated from each other and move more freely around the liquid. The flexibility of a piece of metal is explained in terms of the arrangement of the metal atoms in the semicrystalline structure of the metal, paying particular attention to any defects or departures from a strictly regular form. The temperature of a substance can also be regarded as a dispositional property as it is the ability to transfer heat to neighbouring bodies, but it can be e