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Chapter 4

Explanation and Cause

x4.1 Explanation

x4.2 Why?

x4.3 BeCauses

x4.4 Hume on the Meaning of Cause

x4.5 The Concept of Causal Cause

x4.6 Causal Necessity

x4.7 The Epistemology of Causal Laws

x4.8 Discovering Causal Connexions

x4.9 Causal Reductionism

x4.1 Explanation

Explanation plays a fundamental role in our understanding of rea-son and reality. \Inference to the Best Explanation" is a form ofreasoning we often adopt, the cogency of which has been defendedagainst the sceptics. It is also a mark of reality.1

The search for the ultimate explanation of all things is a drivingforce in intellectual enquiry. But our ordinary ideas of explanationare confused. We are not clear whether it is only something psy-chological, or is a deep feature of the nature of things. Although inthe preceding chapters we have encountered di�erent sorts of ex-planation, we sometimes are impelled to hold that there is au fond

only one basic type of explanation, to which all others should be,in principle at least, reducible. And if there are several varietiesof explanation, we are unclear how they are related. Can di�erentsorts of explanation be compatible, if they are genuinely di�erent?Or do some supersede others, or undercut them?

1 item 6 in lists in x8.2, pp.225 and 228.

100

x4.2 Explanation and Cause 101

x4.2 Why?

Explanations are answers to questions, in most cases the question`Why?' It is, as we have seen, a question easy to ask but di�-cult to answer, even if, unlike the sceptic, we are willing to waitfor one. One fundamental reason, to which I shall return later,is that since explanations are answers to questions, and questionsdepend on the concepts used in formulating them, and since, aswe have seen, the range of concepts available to us is open-ended,the range of possible explanations is open-ended too.2 Even withunproblematic concepts, it is often di�cult to know what sort ofanswer is being sought. Much depends on the exact form of thequestion: the question: `Why are you here?' looks for a di�erentanswer from the question: `Why are you here at the same timeas me?'3 Equally important are the assumptions about what canbe taken for granted and about what we think needs explaining:sometimes it is enough to explain that the event being asked aboutis fairly typical, the sort of thing that often happens; but anotherquestioner may be asking why there should be such a regularity.In the ancient world it was taken for granted that things fell, andonly when arrows and javelins went upwards were special expla-nations called for, and given in terms of some inertial force. If anexplanation was demanded for the regular tendency of things tofall, it was couched in terms of the natural nisus|things had to goto their proper place, which was somewhere below where they werenow. It was Galileo's great achievement to reverse this assumption,and to maintain that being at rest or moving in a straight line wasthe natural state of a�airs for a material object, and that it wasdeviations from that natural state which required explanation. Inso far as the javelin went straight, no explanation was called for:what we needed to explain was why the javelin, and all other heavybodies, tended to fall. Newton's universal law of gravitation o�eredan answer, but raised further questions he was unable to answer.Einstein provided an answer, and explained why gravitational masswas the same as inertial mass, by rede�ning straight lines in termsof geodesics in a curved spacetime. Each `Why?' we ask is asked

2 See above, x2.10, and below x4.9, and x13.7.

3 See Peter Lipton, Inference to the Best Explanation, London, 1991, chs.3

and 5, esp.pp.35�., for an illuminating discussion of \contrastive" expla-

nation of a fact set against a \foil".

102 Reason and Reality x4.2

against a background of unasked `Why?'s, and each answer that isgiven to a `Why?' gives room for further `Why?'s.

The context and the interests of the questioner are also impor-tant. In a law court the issue is the ascription of responsibility;the historian is not trying to determine whom to blame, but tounderstand how the fears and intentions of many men conducedto a particular outcome. Di�erent emotional attitudes to eventsgive rise to di�erent intellectual thrusts in demands for explana-tion. Unwelcome events are ones where we are disposed to wonderwhether they had to happen; in asking `Why?', we are seekingreasons why they had, necessarily, to happen: with other surpris-ing cases we may be concerned only to work out how such an eventcould possibly have happened|particularly in history, we are oftenconcerned to answer \How possibly?" questions rather than \Whynecessarily?" ones, as Professor Dray calls them,4 The di�erencebetween \Why, necessarily?" and \How possibly?" questions is ofgreat importance in metaphysics too. Often we feel that there mustbe an answer to a \How possibly?" question, for else the universe ismysterious and irrational. But it is easy then to slip into thinkingthat the answer is an answer to a \Why, necessarily?" question,and conclude that everything must be as it is, and that there isno freedom for us to order our a�airs as we think best. Many ar-guments for determinism are based on some equivocation between\How possibly?" and \Why, necessarily?" questions, and we shallneed to keep the distinction clearly in mind when unravelling thedi�erent arguments for reductionism.5

4 W.H.Dray, Laws and Explanation in History, Oxford, 1957, ch.6; and

W.H.Dray, \Explanatory Narrative in History", The Philosophical Quar-

terly, 4, 1954, pp.15-27.

5 See below, x13.7.


x4.3 BeCauses

Aristotle distinguished four beCauses.6

Aristotle's Four BeCauses:1. Material2. Formal3. E�cient4. Final

These sorts of explanation are among those we commonly use. Weexplain why something is blue by saying that it is made of coppersulphate. Biologists use Formal7 explanations when they classifyspecimens, and doctors when they diagnose diseases. Aristotle'sE�cient explanation, when we explain an e�ect by citing an an-tecedent cause that made it happen, is mis-termed: `e�cient' has adi�erent sense in modern English; Aristotle uses the word �o� �o�o��

(to poioun) the making or maker. Modern philosophers speak ofa \causal" explanation, which is often held to be the pre-eminenttype of explanation. Biologists often explain organs by referenceto the function they perform, and many human actions can be ex-plained by their purpose, or the end they were intended to achieve.These Final beCauses are now known as teleological explanations.

Formal explanations have been criticized as not being informa-tive: \Why does opium send you to sleep?" \Because it has avirtus dormativa." does not give the questioner the answer he waslooking for. But often to identify and classify is informative. Thedoctor's diagnosis can be re-assuring, even though it does not ex-plain why the disease produces the symptoms it does, and by itselfo�ers no cure. Taxonomy is a respectable part of biology, geologyand chemistry. It does not explain everything, but is a necessary�rst step to formulating further questions.

Aristotle sometimes seemed to think that all human action wasdirected towards achieving some end, but this was a mistake. Wesometimes act rationally|in expressing gratitude, for example|without having any ulterior motive: we should, therefore, recogniserational explanations|why someone did something|as a separate

6 Aristotle Physics II,3, esp. 194b15-195a26 or Metaphysics IV,2; 1013a24-

b28; see W.D.Ross, Aristotle, London, 1923, pp.71-75.

7 from Plato's theory of Forms: Phaedo 97b-99c.


type of explanation, not always to be subsumed under teleologicalexplanation. Many thinkers, however, are reluctant to accept ra-tional explanations as a separate category. It is easy to be cynicalabout gratitude, and explain it a means of securing further favoursin the future. There are, however, other actions and beliefs whichit is di�cult for the cynic to explain away in terms of ulterior mo-tives. But these, it is maintained, can be reduced to a purely causalexplanation. After all, if a man acts out of gratitude or righteousindignation, we can say that his gratitude or indignation made himact as he did. But it is a di�erent sort of `make' from the `make' ofcausal causes. The di�erence becomes apparent if we consider ourreaction to counter-examples. If there is a well-established counter-example to some causal law|if we put a kettle on the �re and itdoes not boil|we have to revise our laws of nature. But if I fail toshow gratitude, no great theories are in jeopardy; it is just that Iam not the man people thought I was, but simply a weak, ungrate-ful specimen of humanity. \The heart is deceitful above all things,and desperately sick" men say of me when they hear of my ingrat-itude. In making up my mind to do something, I remain free, untilI have actually done it, to change my mind. Rational explanations,therefore, are di�erent from causal ones.8

We need to expand Aristotle's list further. Explanations varydepending on the focus of the question. A good example is fur-nished by the bagatelle arrangement in the �gure on next page.

Thermodynamics depends essentially on considering not indi-vidual molecules, but ensembles of them, and calculating the sta-tistical properties of large numbers of un-itemised molecules. Sim-ilarly in a running stream, we do not want and are not able totrack the movement of individual molecules of water, but note thecontinuing existence of certain eddies or whirlpools, and may seekand �nd explanations of these. Often we shift the focus of ourquestions without realising it. The di�erence between biologicaland physical explanation is largely a di�erence of focus. The biol-ogist focuses his attention on organisms, populations and species,concepts of which the physicist knows nothing, while the physicistconcentrates upon atoms and waves, which to the biologist are onlyof marginal concern.

8 This point is well made by G.H. von Wright, \The Logic and Epistemol-

ogy of the Causal Relation", in P.Suppes, et al., eds. Logic, Methodology

and Philosophy of Science, Amsterdam, 1973; reprinted in E.Sosa and

M.Tooley, Causation, Oxford, 1993, ch.6, pp.105-124, esp.x10, pp.121-124.


Bagatelle Balls

Bagatelle balls are introduced at the top of a board, and run down through rows

of more or less evenly spaced pins, and are collected in boxes at the bottom

of the board. If we ask where individual balls will go, or, after the event, why

a particular ball ended up in a particular box, we can give no explanation.

But if we ask about the collective distribution, we can both predict, with

overwhelming probability, and ex post facto explain, its over-all Gaussian

shape.

Thus biologists explain the oscillations in populations of preda-tors and their prey, say Canadian lynxes and hares, in terms ofshortage of food resulting in a reduction of the size of the lynxpopulation, which then allows the unpredated hares to multiply,thereby inducing an explosion in the size of the lynx population.9

The explanation is convincing, but it is di�cult to see how it couldbe \reduced" to a chemical or physical one.10

These di�erent types of explanation have been described as\bottom-up" and \top-down" causation.11 The jaws of a workertermite are extremely well constructed. If we ask `why?', we shallbe told by the biochemist about the properties of the proteins of

9 J.Dupr�e, \The Disunity of Science", Mind, 92, 1983, pp.321-346.

10 See below, x4.9 and x13.7.

11 I am indebted to Arthur Peacoke for this point, which he made in pri-

vate conversation. See further, A.Peacocke, Theology for a Scienti�c Age,

Oxford, 1990, esp. ch.3, x3.2.b, pp.57-58. See also D.T.Campbell, \Down-

ward Causation in Hierarchical Systems", in F.J.Ayala and T.Dobzhansky,

Studies in the Philosophy of Biology, London, 1974.


which they are composed. The biologist, however, will tell a di�er-ent story, about how natural selection has favoured those organismswith the jaws best suited to their life-style. Each of these accountsis explanatory. Both are talking about the same part of the mate-rial universe, but are giving di�erent sorts of explanation, becauseof the di�erence of concepts employed.

The dependence of explanations on concepts is of crucial im-portance. Explanations are answers to questions, and questionsdepend on the concepts used in formulating them, and if, as I shallargue,12 the range of concepts available to us is open-ended, therange of possible explanations is open-ended too.

If there are irreducibly di�erent types of explanation, there arecorrespondingly irreducible di�erences of inexplicability. It is easynot to realise this, because we often use the positive word `random',not realising that it is an essentially negative concept, opposed to`explicable'. Arguments against free will often turn on an equivo-cation in what is to be accounted random. No defence of free will,it is alleged, can be based on the indeterminism of quantum me-chanics, since if it were the case that micro-processes in our brainswere random, our actions would then be random, and not ones wecould be held responsible for. Thus Professor Dennett argues:

The Libertarian could not have wanted to place indeterminism at the

end of the agent's assessment and deliberation. It would be insane

to hope that after all rational deliberation had terminated with an

assessment of the best available course of action, indeterminism would

then intervene to ip the coin before action . : : : 13

But the explicability that quantum mechanics denies is some sort ofphysical explicability, whereas the explicability that responsibilityrequires is a rational explicability, in which the agent explains hisactions and the reasons for them. These are very di�erent types ofexplanation, and it is not to be assumed that the absence of oneimplies the absence of the other.14

12 x4.9.

13 D.Dennett, Brainstorms, Brighton, 1981, and Penguin, 1997, p.295.

14 See below, x13.4; see also J.R.Lucas, The Freedom of the Will, Oxford,

1970, pp.55-59, 109-110.


Questions about Explanantion

1. Is Aristotle's list complete? No2. Are there only a limited number of types of explanation? No3. Can all explanations be reduced to explanations of one type?

No4. Does there being an explanation of one type preclude there

being an explanation of another type? No

x4.4 Hume on the Meaning of Cause

Hume complained that he had no idea of cause, since he could haveno impression of one. But we do have a concept of cause. We usethe word frequently, and though we may be at a loss to give an exactaccount of its meaning, we think we have a rough understandingof what we mean. Hume confused the concept of cause with theconditions of its application. Both were called \ideas". But my ideaof causality|of what it is in general to be a cause|is quite di�erentfrom its application in a particular case| my idea that this eventis the cause of that. My entitlement to say that this event is thecause of that rests upon various statements in the indicative moodin the past and present tenses: but the concept of cause involvespredictions in the future tense, necessity, and certain counterfactualconditionals. I base my assertion that cyanide causes death onreported instances of death following the ingestion of cyanide: butin actually making the assertion, I predict the outcome of peopletaking cyanide in time to come, impute to it some natural necessity,and commit myself to a number of counterfactual conditionals tothe e�ect that if such and such a person were to take cyanide, hewould die.

Hume's account of the meaning of cause yields further insightinto the meaning of meaning, and clinches the refutation of theVeri�cation Theory of Meaning in Chapter One.15 It shows thatconcepts are di�erent from conditions of application. The evidencefor a causal claim must be expressed in the indicative mood and inthe present and past tenses, but the content of the claim goes intothe future tense and into other moods than the indicative. In goingfrom the evidence to the conclusion that C causes E, we are going

15 x1.2.


Hume on CausalityHume makes two valid points about causal connexion:1. There is no analytically necessary connexion between cause

and e�ect;2. The connexion between cause and e�ect is not perceived by

the senses.|o0o|

Hume has run together two di�erent questions:1. What does `cause' mean? (What is our idea of causality?)2. What are the conditions under which the term can be cor-

rectly applied? (When are we entitled to have the idea that

A is the cause of B?)(1) is an analysis of the concept of cause; (2) is an account ofthe criteria of applicability. The word `idea' can mean eitheran idea of (a concept) or an idea that (a proposition).

beyond what we are given, and are sticking our necks out. This isa paradigm instance of the claim made in Chapter One,16 that wetypically make statements that go beyond the evidence for them.The Veri�cation Theory of Meaning is entirely misconceived. Itcannot accommodate predictions, statements about other minds,or unobserved objects, it gives a distorted account of causality,and|perhaps the most convincing example of its inadequacy|itcannot account for simple mathematics.

According to the Intuitionists|the Veri�cationists in the phi-losophy of mathematics|the meaning of a mathematical propo-sition is given by its \assertibility conditions". But many peopleknow Pythagoras' theorem, while �nding it di�cult to prove. Arewe to say that they do not know Pythagoras' theorem|not evenif they use 3-4-5 triangles to mark out a tennis court|unless theycan produce one of the forty seven proofs of the theorem? And canwe make sense of there being di�erent proofs of the same theoremunless the meaning of the theorem is separable from that of theproof? I can understand Fermat's Last Theorem though I can-not understand Andrew Wiles' proof of it. Those mathematicianswho can understand it no doubt have a deeper understanding thanthey did before. But they understood well enough what the the-orem stated to be excited at the news of its being proved. And

16 x1.2, pp.7,8.


it is di�cult to understand what Wiles himself was doing in theyears he spent looking for a proof, if he could not know what hewas looking for until he had found it.

A similar mistake is made in arguing for the Frequency Theoryof Probability. The evidence on which probability judgements arebased is, very often, the frequency of some sort of occurrence withinan observed collection of instances. But to maintain that this iswhat probability judgements mean leads to absurd complications.Similarly it has been argue

x4.5 The Concept of Causal Cause

Once we accept the point that the meaning of a word may be di�er-ent from the criteria for its correct application, Hume's di�cultiesno longer worry us. But still, we may ask how we come by theconcept, and how it is related to other concepts we ordinarily use.

In our everyday life as agents we often bring things about; wemake things happen and sometimes prevent things happening thatotherwise would have happened. I make the pot boil, or, moregrandly, I cause the pot to boil, by putting it on the �re; and youtake care, by placing a �reguard in front of it, that the �re does notset the furniture alight. Often we have to use appropriate meansto bring about desired ends. I light the �re by selecting dry woodand tinder, and getting them alight before putting on damp logsfrom the woodstack. We �nd it natural to say that we causedboth the intermediate means and the ultimately desired state ofa�airs, and to construe the verb `to cause' as expressing a transi-tive relation: I caused the pot to boil by causing a match to ignite,which caused the kindling to catch �re, which caused the �re toburn, which caused the pot to boil. We attribute to the interme-diate means the same causal powers as we exercised ourselves inbringing about those means, and through them the ends that wesought to achieve.17 The notion is crude, and a determined analystcan subject it to the death of a thousand questions. It remains,however, crudely robust. Rather than querying it away, we should

17 G.H.von Wright uses the word `manipulate', which expresses the point

well; we manipulate means so as to bring about the desired end. See

his \The Logic and Epistemology of the Causal Relation", in P.Suppes,

et al., eds. Logic, Methodology and Philosophy of Science, Amsterdam,

1973; reprinted in E.Sosa and M.Tooley, Causation, Oxford, 1993, ch.6,

pp.105-124, esp.xx8,9, pp.118-121.


accept it as useful, repair its inadequacies, and re�ne it, when nec-essary, to occupy a comparable position in our more sophisticateddiscourse.

The concept of cause I acquire through myself causing things tohappen is temporally directed, explanatory, local and singular. Iinitiate action, typically bringing about my ultimate end by inter-mediate means, and the reason why it happened is that I decidedthat it should. Causes come before their e�ects, are spatiotempo-rally connected with them, and to a limited extent explain whythey come to pass. Causal explanation implies temporal priority.Explanations need to be informative, and therefore compact. In thelanguage of Cybernetics, they need to have more negative entropythan what they are explaining. I can explain the ripples on a pondby there having been a stone thrown in, but if I reversed the direc-tion of time, and tried to explain them by a fortuitous harmony ofmovements at the pond's edge conspiring to create concentric rip-ples all converging on a centre so as to propel a stone upwards andaway from the pond altogether, my purported explanation wouldlack explanatory force because it stood more in need of explanationthan what it was supposed to explain.

Causes can be singular. Davidson is right in holding, againstthe opinion of most philosophers, that a singular causal relationis perfectly intelligible.18 The concept of a singular one is intel-ligible. Quite apart from the cases where I did it, or you tell methat you did it, some primitive tribes are animists and ascribeagency|which may be completely arbitrary|to everything. Itmay be superstitious and mistaken, but it is perfectly possible tothink that all events are the actions of deities. I forgot to clean myteeth this morning, so the gods made me fall down as I ran acrossthe playground, and graze my knee. Events cause other events, inaccordance with the inscrutable ordinances of the gods, who maysometimes overlook my misdemeanours, and on other occasionsvisit my innocent actions with penal consequences. Singular cau-sation is a coherent concept, and can be defended on metaphysicalgrounds. Some philosophers seek to explicate time in terms of it.Indeed, granted very few additional axioms, it is possible to derivethe Special Theory from a simple transitive asymmetric spatiotem-porally continuous causal relation.19

18 D.Davidson, \Causal Relations", Journal of Philosophy 64, 1967, pp.691-703; reprinted in D.Davidson, Essays on Actions and Events, Oxford, 1980;and in E.Sosa and M.Tooley, Causation, Oxford, 1993, ch.4, pp.75-87.

19 See further below, x10.2.


Sources of our concept of causal cause

1. First-personal experience of making things happen.

Although intelligible, the concept of a singular cause is di�cultto use. The inscrutable ordinances of the gods are inscrutable, andalthough someone might have privileged access to their counsels,in practice we need less arcane knowledge if we are to be able tochart our course in the secular world. If I am to achieve my endsby bringing about the appropriate means, I must be able to reckonthat means of a recognisable sort will result in a state of a�airs ofa sort that I do want to obtain. Otherwise I could not cause endsto occur by causing the appropriate means. Admittedly, life mightstill be possible: there are primitive tribes who sow seeds becausethat is the right thing to do in spring, and gather harvest becausethat is what is always done in autumn; but then we say that thesetribes have no concept of cause and e�ect. To have the concept andbe able to use it, one must be able to generalise|to universalise|a little, and reckon that things of this sort cause consequences ofthat sort. At least so far as macroscopic natural phenomena areconcerned, we apply and understand causes and e�ects as instancesof general types that are connected by some causal law.

Generality is implied not only by the practical requirements ofmanipulability, but by the desire for explanation. We not only usecausal causes to make things happen, but invoke them to explainwhy things happen. Even in the superstitious example there wassome suggestion of failing to clean one's teeth each morning beingbad: although the gods might have made me fall down in the play-ground, because I had done my morning exercises, or because I haddone my homework last night, I should be so much at a loss tounderstand why these virtuous activities should have been visitedwith untoward consequences, that I should not pick them out aspotential causes of my misfortune. If causal causes are to explain,they must identify some antecedent condition as the sort of thingthat could be a cause; causes we can discover and use must in someway be universalisable. Thus though singular causes are logicallypossible|it does make sense to say that this caused that|thereare strong conceptual pressures in favour of some sort of generality.


1. First-personal experience of making things happen.2. Explaining why things happen.


The concept of cause I gain from my �rst-personal experienceof making things happen carries with it a notion of necessity. Butmeans are third-personal. What sense can I give to the meansbringing about the ends? They have no purposes, and form nointentions. But they can necessitate. The �re has no intention ofmaking the pot hot, but it makes it hot all the same. Under normalconditions, if the pot is put upon the �re, it cannot be otherwisethan that the pot gets hot. Causal necessity implies universality,but is more than it. Necessity is what distinguishes causal lawsfrom accidental generalisations. It might just happen to be thecase that every time I had spilt the salt, I had subsequently su�eredbad luck, but I could still maintain that it was only a coincidence,and deny that spilling the salt caused the bad luck. To claim thatthere was a causal connexion, I should have to claim not only thaton those occasions when I actually spilt the salt, I subsequentlysu�ered bad luck, but that on any other occasion, if I had spiltthe salt, then I would have su�ered bad luck. To assert a causalconnexion is to go beyond the actual, and to make claims aboutpossible cases as well. The counter-factual `if I had spilt the salt,then I would have su�ered bad luck' follows from `my spilling thesalt necessitated my su�ering bad luck', but not from `wheneverI spilt the salt I actually did su�er bad luck'. The necessity ofcausal laws follows also from their ambition to explain. Althoughsometimes the question being asked is a `How possibly?' ratherthan a `Why necessarily?' one, the modal force of rationality isusually towards necessity rather than possibility. We understandwhy something happened by coming to understand why it had tohappen.


1. First-personal experience of making things happen.2. Explaining why things happen.3. Third-personal experience of means making ends happen.


x4.6 Causal Necessity

Someone might protest, on behalf of Hume, that he had no ideaof causal or natural necessity: the concept was not one he hadbeen able to take on board. An explanation is owed of how wecome by such a concept. Although Hume was right to point outthat causal necessity is not logical (analytic logical) necessity, andthat we cannot acquire the concept of causal necessity from simpleimpressions alone, he was wrong to despair of our ever being ableto have the concept of causal necessity at all. It can be extrapo-lated from our �rst-personal experience. I make things happen. Ihave a concept of things being made to happen, and can apply itwhere it is not I who have made something to happen, but some-thing else, ascribing to it a power I know myself to have. Modernphilosophers are queasy at such anthropomorphism, but toy withthe possibility that we have an \innate idea", that we had evolvedso that our brains were wired up in such a way that we instinc-tively sought causal connexions, and jumped to conclusions whenthe evidence provided us with a springboard, in the same way aswe seem to be hard-wired to be able to learn languages. Psycholo-gists might be able to devise experiments to determine whether thiswas the case.20 If a sense of causal necessity is innate, it could bethe case that some people are born without it, in much the sameway as some people are born without being able to discriminatered from green. This would explain why Quine and many othermid-twentieth-century philosophers reported that they could notunderstand what `causal necessity' or `natural necessity' meant.

Less problematic is the suggestion that we learn to apply causalconcepts by trial and failure: we learn that no matter how hard we

20 Compare J.L.Mackie, Problems from Locke, Oxford, 1976, ch.7, p.211, \at

the core of <causality> there is the notion expressed by the counterfactual

conditional, the notion of what would have happened if this had not, and

I have argued that this arises primitively from imaginative projection and

analogizing; our tendency to do this and hence to think causally may well

be another inborn propensity." See also J.L.Mackie, The Cement of the

Universe, Oxford, 1974 (pbk. 1989), pp.55-57; see also, Peter Lipton, In-

ference to the Best Explanation, London, 1991, pp.6-8,15-17; N.Chomsky,

Aspects of the Theory of Syntax, Cambridge, Mass., 1965 ch.1, x8, esp.

pp.58-59, N.Chomsky, Knowledge of Language, New York, 1986; T.Kuhn,

The Structure of Scienti�c Revolutions, Chicago, 1977; and T.Kuhn, The

Essential Tension, Chicago, 1977, esp. chs. 1 and 2.


try, some concatenations of events cannot be brought about, andhence, equivalently, that others are inevitable: if no matter howhard I try, I cannot immerse my hand in water without its gettingwet, then I know also that the truism \water wets" is an unavoid-able law of nature. Although we cannot see necessity, we can learnit from unsuccessful experience. It is a concomitant of our activityas agents. I try, and not succeeding at �rst, I try and try again.But if, whatever I do, and however much I try, I still do not suc-ceed, I generalise from these particular failures, and conclude thatI shall always fail: I cannot succeed, because it is impossible. I maybe wrong, but the conclusion is intelligible enough to give contentto a concept of natural impossibility, and hence of natural neces-sity, distinct from the impossibility and necessity that arises fromdeductive logic. In particular, if certain conjunctions|A withoutB, taking cyanide and not dying|appear to be impossible, we canreformulate in terms of necessity, and say that A necessitates B,taking cyanide necessarily is followed by death. We thus have a con-cept of necessity which we can apply not only to occasions when wecause things to happen, but to occasions when things themselves|or events, or whatever|cause other things to happen.

The rational necessity cited in the previous section is a re-spectable concept. It is only in a very limited sense of `logical'that there is no logical necessity for a cause to be followed by itse�ect. True, there is no inconsistency in supposing the cause notto have been followed by the e�ect: it is not a breach of the rulesof language to speak of the cause not being followed by the e�ect.But once we move on from �rst-order logic, logical necessity is notcon�ned to analytic necessity. We use the word `logic' in a varietyof senses to mark a variety of contrasts. Thus in a passage quotedin the next section (x4.6) Tolman contrasts the inner logicality ofthe Special Theory with experimental veri�cation, where logicalityembraces much more than �rst-order logic: the Special Theory isto be adopted on grounds of symmetry, continuity and consiliencewith other theories.21 These a priori considerations not only leadus to adopt the theory, independently of empirical evidence, butconfer on it a sense of somehow being necessarily true, and hencealso on any conclusions drawn from it. Many people have thoughtthat Newtonian mechanics was necessarily true|Kant o�ered ar-guments purporting to prove it. Believing that, they have believed

21 R.C.Tolman, Relativity, Thermodynamics and Cosmology, Oxford, 1950,

x29, p.53, quoted in x4.7, ad �n. on pp.119-120 below.


that if one croquet ball hits another, that other one must be movedby the impact. Empiricists may contend that the a priori consider-ations adduced by Kant and others are fallacious. Suppose, for thesake of argument, that they are right: that would only show thatmany people were wrong in their attributions of necessity, not thatthey did not have the concept. I may believe Newtonian mechan-ics on the authority of my school teacher, not on account of anyobservations I have made or heard about. But I still shall thinkthat momentum must be conserved, even though my warrant forso believing will not stand up to sustained criticism. I shall havethe concept of causal necessity, even though I am not, according tothe empiricists, applying it correctly. Di�erent people may acquiretheir notions of necessity in di�erent ways: but the obligation toexplain how we could come by such a notion has been discharged.Some people may still claim not to be able to understand causalnecessity, but must speak for themselves alone.

Sources of necessity

1. First-personal experience: I made it happen.2. Innate (hard-wired) intellectual re ex (Compare Chomsky).3. Trial and failure: impossibility is necessity's other face.4. Rational necessity of consequences of an accepted explana-

tion.

We can give content to the concept of causal necessity, but it isanother matter to justify the inference from a bare generalisationto a modal conclusion. Although in practice we seldom have anydoubts, in principle it seems a hazardous step to go from a simplegeneralisation

(8x)(A(x)! Z(x))

to a causal law, perhaps expressed by a modal proposition

(8x)(A(x)! Z(x))

where is some sort of natural or causal necessity. One justi�cationis that if a generalisation is due to a causal law, the generalisationis explained. It is not just an accidental happenstance, but an un-derlying feature of the universe that we have come upon. There


is a parallel with sense data and material objects.22 At �rst sightwe may have di�culty in making sense of a scene, but if we canconstrue a jumble of edges and surfaces as aspects of a buildingseen from a strange angle, we can comprehend the whole, and seeit all as it is. Causal connexions are four-dimensional analoguesof material objects. Instead of solidity and impenetrability, theypresent necessity and ineluctability, and, once posited, make senseof otherwise disparate phenomena. Often the causal law �ts inwith other laws we have already discovered; our knowledge of na-ture is cumulative; we can apply causal principles we have alreadydiscovered to assess not only the relevance of some factors, but theplausibility of some proposed generalisations.

The inference from a simple generalisation to a causal law.though hazardous, can be defended; but always there is the wor-rying possibility that our generalisation is only a coincidence, andthere is no causal connexion at all. This worry we often resolveby experiment. We contrive to bring about A when it otherwisewould not have occurred, and see whether it is accompanied orfollowed by Z: if it is not, we have falsi�ed the putative general-isation, (8x)(A(x) ! Z(x)) and can end that line of enquiry; ifit is accompanied by Z, we become con�dent that we are deal-ing with a causal law, not just a coincidence. Our reasoning isthat our intervention was entirely external to the course of eventswe were examining, and any chance concomitances they may havepresented. It might conceivably have been the case that the initialstate of the universe happened to be one in which every occurrenceof A is accompanied or followed by Z; but we have now intervenedde novo, thereby disrupting any chance concomitances there hap-pened to be. Anything that survives our interventions is solid, justas resistance to our probing with a stick enables us to feel out theshape of objects at the bottom of a muddy pool.

The argument from experiment assumes free will on the partof the experimenter. On a determinist view of the world, the ar-gument is open to the objection that the same antecedent con�g-uration of the universe that resulted in the experimenter alteringthings so as to bring about A, had as its consequence also that Zshould occur too. In a determinist universe the long arm of coinci-dence could extend through the experimenter's mind to have himchoose to make A happen on just the occasion when Z was goingto happen anyway. Determinism, we shall argue later, is false.23

It is desirable that it be false for many other reasons, but also forthis ironical one, that it is only on the assumption of its falsity thatwe can assure ourselves that seeming causal laws really are causallaws, and not accidental generalisations.

22 See further below, x6.7.23 In x13.4.


x4.7 Causal Reductionism

Although philosophers are ready to admit that there are manydi�erent types of explanation, they often suppose that one typeis pre-eminent. Collingwood argues that some sort of �nal cause,as in \woman with a cause", is basic, and the modern sense ofcausal cause a late (and regrettable) development.24 But mostphilosophers have held that causal causes are pre-eminent. Leibnizdiscusses Snell's Law of refraction and points out that Snell andFermat derived it from the principle of least action:25 \For whenthe rays observe in the same media the same proportion of the sines,this is found to be the easiest way, or at least the most determined,for passing from a given point in one medium to a given point in theother."26 Leibniz claims that this is an instance of a �nal cause; andwhile allowing \that the way of e�cient causes : : : is indeed, deeperand in some fashion more immediate and a priori", reckons that\the way of �nal causes is easier, and is not infrequently of use fordiscerning important and useful truths which one would be a longtime in �nding by the other more physical route, . . "27 Leibniz iswrong to see the principle of least action as a �nal cause, thoughright to note the importance of extremal principles as a form ofexplanation, which can be derived from causal explanation. Finalcauses can, however, be sometimes explained in terms of causalcauses. Darwin's theory of evolution gives a schema for showinghow �nal causes could be explanatory in a world that was entirelygoverned by causal laws.

The question arises whether the reductions outlined by Leib-niz and Darwin can be extended to cover all forms of explanation.Can they all be reduced ultimately to causal explanation? Manythink they can. F.H.C. Crick, maintains \the ultimate aim of themodern movement in biology is in fact to explain all biology interms of physics and chemistry".28 Many biologists oppose such aprogramme, and often scarcely bother to argue against it, rejecting

24 R.G.Collingwood, Metaphysics, Oxford, 1940, Part IIIc, chs.XXIX-XXXII,

pp.155-176.

25 Leibniz, Discourse on Metaphysics, chs. XIX-XXII, tr. P.G.Lucas and

L.Grint, Manchester, 1953, pp.32-40.

26 ch.XXII, p.39.

27 pp.38-39.

28 F.H.C.Crick, Of Molecules and Man, Seattle, 1966, p.10.


it as obviously ridiculous. Their experience of their own disciplinesconvinces them that the explanations o�ered are quite all right asthey stand, and in no need of being validated by being shown to bereally special cases of some other sort of explanation. More thanthat, they hold that reductionism impugns the autonomy of theexplanations they actually o�er, and in some way undercuts theirvalidity. Like the reductionists, the anti-reductionists adduce anargument from the success of science: the natural sciences otherthan physics have been very successful; they have been able to ex-plain and illuminate our understanding. Other biologists, however,feel threatened by the claim that in principle all the things a biol-ogist studies are completely explicable in terms of chemistry andphysics. Even if in practice we accept that there are many di�erenttypes of explanation, and use those explanations that are appropri-ate to the discipline and the problem under consideration, we areuncomfortable, at least in our metaphysical moments, with theirindependent co-existence, and feel that in the ultimate analysis theexplanations provided by the physicists must be all-embracing, andmust furnish us with a complete explanation of everything.

Metaphysical doctrines are at work. The `must' is a metaphysi-cal must, which overrides all contrary evidence of explanations thatseem to resist reduction to physical ones. It is in part an ontologi-cal claim, about the nature of reality. the discussion of which mustbe deferred until Chapter Nine, in part a conceptual claim, aboutthe nature of explanation, holding that in principle all explana-tions can be derived from a fundamental causal explanation. Cer-tainly, with some explanations it is possible. There have been somesuccessful reductions. Thermodynamics has been reduced Statis-tical Mechanics: granted Newtonian mechanics, some assumptionsabout the shapes and elasticity of molecules, and simple statistics,we can o�er de�nitions of the concepts, and derive the principles ofthermodynamics in an illuminating and satisfactory way. Geneticshas been similarly reduced to the biochemistry of DNA. There havebeen many more partial reductions. The chemistry of the hydro-gen atom has been largely explained by quantum mechanics. Weunderstand some physiological processes because we understandthe biochemistry of the reactions involved. The Logicists devisedde�nitions of mathematical concepts in terms of simple logic; andeven though the Logicist programme has been beset by problems,and cannot be adjudged a complete success as yet, it may still beamended and carried through to a successful completion. Similarly,


it is claimed, for all other disciplines. This is the doctrine of Phys-icalism. It is a doctrine of explanatory reductionism, holding thatall other forms of explanation, useful though they may be in par-ticular contexts, can be derived from physics, and are, essentially,only special cases of physical explanation.

But explanations are answers to questions, and so depend onthe concepts used to frame the questions, and scientists do notnaturally have the concepts of other sciences|it takes time to learna science and to grasp its concepts. The weakness of conceptualreductionism is well put by Christopher Longuet-Higgins:

In recent years there has been much interest among chemists in what

are now called electrocyclic reactions : : : Along comes a physicist, ex-

pert in quantum mechanics, which, he maintains, explains all chem-

istry in principle, and we ask him for an explanation of electrocyclic

reactions. Does he o�er one? No. His �rst words are `What are elec-

trocyclic reactions?'. In order to answer the question, we shall have to

introduce him to chemical concepts that are not part of his intellec-

tual armoury, and even then he may not understand why we asked the

question. Actually to answer it he has to become, for the moment at

least, a chemist. Only by so doing can he see what principles of physics

may be relevant to its answer. Insofar as physics is what physicists do

when they are left to get on with their own work, chemistry is not part

of physics in any important sense. It has its own concepts and its own

problems, the concepts being those that are relevant to the problems.

This, of course, is not to deny that physical principles can be brought

to bear on chemical phenomena, but the questions must be asked at

the higher level before they can be examined at the lower.29

Longuet-Higgins argues by example, and there are many others.Even within physics there are many concepts that could not bereduced to more basic ones. In the nineteenth century, it was of-ten felt that we should not be able really to understand electro-magnetism, unless we could produce a \mechanical" model, andmuch work was devoted to models of the ether as an elastic jelly-like medium. In the end the concepts of electromagnetism werenot \reduced" to those of Newtonian mechanics, but what shouldcount as a physical concept was enlarged so as to include those of

29 H.C.Longuet-Higgins, The Nature of Mind, Edinburgh, 1972, ch.2, pp.16-

21, esp. p.19; reprinted in H.C.Longuet-Higgins, Mental Processes, Cam-

bridge, Mass., 1987, ch.2, pp.13-18, esp.p.16.


electromagnetism. Even the example of thermodynamics is two-edged. Entropy cannot be explained simply by considering justone Newtonian system; rather, we have to consider an \ensemble"of them, and ensemble is not a Newtonian concept.30

For many thinkers the examples are decisive. But in our meta-physical moods, we may feel that they are not conclusive: at somefuture time, a cleverer thinker may devise adequate de�nitions ofthe concepts of each discipline in terms of those of a more basicone, so that in the end the physicalist programme may be carriedthrough.

It is di�cult to argue with may-bes. But we can show that themetaphysician's may-be cannot be universally successful. As withthe hoped-for reduction of mathematics, the clinching argument isto be found in logic. Tarski showed that the concept of truth couldnot be expressed in a formal system of logic that met reasonablerequirements of consistency and adequacy.31 Hence, contrary tothe teaching of many Positivists, truth cannot be de�ned in simpleterms. Reductionism fails in this, crucial and seemingly promising,case, and thus fails to hold universally.

Tarski's theorem is recondite, and of no concern to most workingscientists, who might maintain that the exception to reductionismwas a purely academic one, and that for all practical purposes, re-ductionism still held good. But truth is not of arcane academicconcern alone. The working scientist wants to commend his resultsas being true. Moreover, it is characteristic of human beings gen-erally that they have a concept of truth, and care about it greatly.Reductionists are committed to the claim that it is in principlepossible to explain all human action in terms of fundamental phys-ical laws; but any purported explanation of a particular man's be-haviour can be faulted; for some of the things he can see to betrue are things he ought not to be able to produce as true, if hisoutput was really determined entirely by mechanical causes.32 The

30 Of course, physicalism could be made true trivially, if the concepts ofphysics were enlarged to include the concepts of every science and dis-cipline; but then it would be of no interest.

31 See above, x2.10.

32 \Minds, Machines and G�odel", Philosophy, XXXVI, 1961, pp.112-127;reprinted in Kenneth M.Sayre and Frederick J.Crosson, eds., The Mod-eling of Mind, Notre Dame Press, 1963, pp.269-270; and Minds and Ma-chines, ed. Alan Ross Anderson, Prentice-Hall, 1954, pp.43-59. See alsoJ.R.Lucas, Freedom of the Will, Oxford, 1970; Roger Penrose, The Em-peror's New Clothes, Oxford, 1989; and Roger Penrose, Shadows of theMind, Oxford, 1994.


argument is controversial, but carries conviction. A rational beingcannot be represented by a Turing machine. Rational beings exist.So reductionism fails.

The argument against reductionism is a conceptual one. Con-cepts cannot always be reduced to more basic ones. And if conceptscannot, explanations cannot either, since explanations are answersto questions, and depend on the concepts used to formulate thequestions. If the concepts cannot be translated into the terms ofa supposedly more basic discipline, the explanations cannot be de-rived from the explanations of the supposedly more basic discipline.

The result is important, but limited. It rules out one sort ofreductionism|explanatory reductionism we might call it|-whichclaims that all explanations can be reduced to one basic form, andin particular, it rules out physicalism, which claims that all ex-planations can be reduced to a Hempelian physical explanation interms of a covering law and initial conditions.33 But reductionismis often driven by ontological, rather than explanatory, considera-tions, holding that there is only one form of fundamental substance,and that everything that exists is merely a modi�cation of that fun-damental substance, and can be completely explained in terms ofit. The arguments of this section do not touch that claim, whichwill be considered further in Chapter Thirteen. They do, however,have one further positive consequence: if explanations depend onquestions, and questions on concepts, and there is no limit to thenumber of new concepts that we may come to have, there is no limitto the number of new questions that we can ask, and hence to theexplanations that we could come to have. Logic rules out there be-ing a Theory of Everything which cannot be further questioned. Ifthere is an ultimate explanation, its ultimacy must depend not onour being unable to raise further questions, but on our not want-ing to, because the explanation already given is so satisfying thatquestions we conceivably could raise no longer worry us.Click here to go to Next ChapterClick here to go to Table of ContentsClick here to return to Home Page

c J.R. Lucas 2006But you are welcome to download a single copy of this for yourown personal use; see, more fully, Copyright Notice

33 C.G.Hempel and P.Oppenheim, \The Logic of Explanation, Philosophyof Science, 15, 1948, pp.135-175, reprinted in H.Feigl and M.Brodbeck,Readings in the Philosophy of Science, New York, 1953, pp.319-352; seealso, C.G.Hempel, \The Function of General Laws in History", The Jour-nal of Philosophy, 39, 1942, pp.35-48, reprinted in H.Feigl and W.Sellars,Readings in Philosophical Analysis, New York, 1949, pp.458-471.

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