Table Of ContentLaws and Symmetry
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Laws and Symmetry
Bas C. Van Fraassen
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Preface
The idea that there are laws of nature is by no means the sole property of philosophers. That this idea is the key to
what science is, often appears as self-evident in popular thought: in The History of Landscape Painting, John Constable
writes‘Paintingisascience’andheadds,unconsciousofanyleapinthought,‘andshouldbepursuedasaninquiryinto
thelawsofnature.’ Thatthese lawsconstitutealsowallsofimpossibilitythatborder thecourse ofevents, is a constant
preoccupation of Dostoevsky's narrator in Notes from Underground: ‘all the same’, he says, ‘the laws of nature have
mistreated me constantly, more than anything else in my life’.
But the idea that there are such laws has also played a major role in philosophy concerned with science. We find this
ideaperhapsmostprominentlyinthephilosopher-scientistsoftheseventeenthcentury,butitsurvivedinourseventhe
logical positivists' radical rejection of history. Reichenbach, Hempel, and Goodman themselves invoked laws to shed
light on issues prominently associated with their names. Their invocation was perhaps critical and tentative, but it
seepedintootherareasofphilosophyascertainty.Whenmoralphilosophersdiscussfreewill,forexample,shouldthey
not be allowed to lean on such certainties as philosophy of science has established concerning cause, necessity,
counterfactuals, and nomological explanation?And similarly, given those supposed certainties, isn'titquite proper too
for philosophy of mind to approach uncritically the question whether there are psycho-physical laws?
In the first part of this book I shall argue that no philosophical accountof laws of nature does or can succeed. In the
second I shallrebut theargumentthatwe must believe inthem nevertheless. Now if thereare laws of nature we must
approach science in one way, but if there are no laws, we are freed to leave behind a whole range of traditional
problems. I make a proposal for how to do philosophy of science, and devote the third and fourth part to
contributions to the semantic approach (as Frederick Suppe baptized it) which I advocate. The emphasis will be on
symmetry, as a key to theory, though not in the sense that laws were.
This book was originally twice as long. When a general approach
viii PREFACE
isannounced and advocated, itremains hand-wavingexcepttotheextentthatitis implemented. Accordingly, thenow
missing part was devotedto a detailed study of the structure and interpretation of quantum mechanics. It will appear
separately, as Quantum Mechanics: An Empiricist View.
My colleagues in philosophyof sciencemay be a littlesurprised by Part I, for the accounts of law taken up belong to
theareaofmetaphysicswhichtheygenerallyignore.Theyareofcoursefreetoignorethatpartandturntothechapters
on inference to the best explanation, theories, symmetry, classical physics, and probability. I too lack sympathy for
metaphysics, though not in general: only for pre-Kantian metaphysics— and then only if practised after Kant. I have
triedtoensureneverthelessthatnoneofmyargumentsrestsonthisrejection;otherwisemycritiquewouldnotbevery
effective.Thosewhodon'tcaretoengagethemetaphysiciansontheirownground,Iwouldliketourgeatleastthis:do
notrelyonsuchconceptaslawwithoutinquiringwhether thereisanythingthatcouldplaytherequiredrole.Forthatis
similar to other philosophers relying unquestioningly on fifty-year-old philosophy of science.
There are many peopleand institutions I want to thank. The original manuscriptwas writtenduring a sabbatical leave
(1986/7) supported byPrinceton Universityand theNational ScienceFoundation. Specific debts are acknowledged in
manysections,butIwishtothankErnanMcMullen,DavidLewis,StorrsMcCall,WesleySalmon,MichaelTooley,and
Richard Foley for special help with Part I. For Part II I want to acknowledge the help and insights received from
GilbertHarman,RichardJeffrey,andBrianSkyrms.ElisabethLloydhelped metoseenew possibilitiesinthesemantic
approachtotheories, and R. I. G. Hughesinthemanyuses ofsymmetry. DiscussionswithBrian Skyrms, Maria-Carla
Galavotti,and Nancy Cartwright helpedwithcausality, while Roger Cooke helped with theintricaciesof bothclassical
mechanics and subjective probability. Joint work withR. I. G. Hughes appears in thelast chapter. Perhaps needless to
say,itwasmyvaluedteacher WilfredSellars andmyeventualcolleagueGilbertHarmanwhostartedmeonthesubject
of inference to the best explanation, a number of years ago. Margot Livesey suggested a good deal of stylistic
improvement in the first three chapters and I hope this had its effect on the later ones as well.
PREFACE ix
Anne Marie DeMeo typed endless drafts of this material over a period of about three years, and kept my practicallife
functioning even while I travelled; she deserves special thanks.
Finally, I want to acknowledge with some nostalgia the places where I wrote the draft during that initial year:
Vancouver, Victoria (BC), Montreal, Notre Dame, Bologna, Assisi, Rome, Jerusalem, Tiberias, Cambridge (Mass.),
Cleveland, and London.
