an introduction to the philosophy of science ........................................................... SCIENCE AND ITS CONCEPTUAL FOUNDATIONS A SERIES EDITED BY DAVID L. HULL THEORY AND REALITY ........................................................... Peter Godfrey-Smith is associate professor of philosophy and of his­ tory and philosophy of science at Stanford University. He is the author PETER GODFREY-SMITH of Complexity and the Function ofMind in Nature. The University of Chicago Press, Chicago 60637 The University of Chicago Press, Ltd., London © 2003 by The University of Chicago All rights reserved. Published 2003 Printed in the United States of America 12 II 100908 45 ISBN: 0-226-30062-5 (cloth) ISBN: 0-226-30063-3 (paper) Library of Congress Cataloging-in-Publication Data Godfrey-Smith, Peter. Theory and reality: an introduction to the philosophy of science I Peter Godfrey-Smith. p. cm. - (Science and its conceptual foundations) Includes bibliographical references and index. ISBN 0-226-30062-5 (alk. paper) - ISBN 0-226-30063-3 (pbk. : alk. The University of Chicago Press / Chicago and London paper) I. Science-Philosophy. I. Title. II. Series. QI75 .G596 2003 501-dc2I 2002155305 @ The paper used in this publication meets the minimum requirements of the American National Standard for Information Sciences-Perma­ nence of Paper for Printed Library Materials, ANSI Z39.48-1992. 38 Chapter Two Schlick's "Positivism and Realism" (1932-33) and Feigl's "Logical Empiricism" (1943) are good statements oflogical positivism by original members ofthe Vienna Circle. (Feigl uses the term "logical empiricism;' but his paper describes a fairly strong, undiluted version ofthe view.) Ayer's Language, Truth, and Logic (1936) is readable, vivid, and exciting. Some see it as a distortion of logical positivist ideas. The Routledge Encyclopedia ofPhilosophy (1998) has an interesting collection 3 of articles, especially in the light of new debates about the history of logical posi­ tivism. The article on logical positivism is by Friedman and reflects his somewhat Induction and Confirmation unorthodox reading (de-emphasizing the empiricist tradition). Stadler's entry on the Vienna Circle gives a more traditional view. See also Creath's entry on Carnap. On all these issues, see also the essays in Giere and Richardson 1997· Peter Galison's ''Aufbau/Bauhaus'' (1990) is a wonderful account ofthe artistic, 3.1 The Mother of All Problems social, and political interests of the logical positivists and the links between these interests and their philosophical ideas. Passmore 1966 is a good and accessible sur­ In this chapter we begin looking at a very important and difficult problem, vey of philosophical movements and trends in the late nineteenth and early twenti­ the problem of understanding how observations can confirm a scientific eth centuries, including absolute idealism. theory. What connection between an observation and a theory makes that Hempel, Aspects ofScientific Explanation (1965), is the definitive statement of observation evidence for the theory? In some ways, this has been the fun­ logical empiricism. His Philosophy ofNatural Science (1966) is the easy version. damental problem in the last hundred years of philosophy of science. This Carnap's later lectures have been published as Introduction to the Philosophy of problem was central to the projects of logical positivism and logical em­ Science (1995). piricism, and it was a source ofconstant frustration for them. And although An attempt to revive some logical positivist ideas has recently begun; see, for ex­ some might be tempted to think so, this problem does not disappear once ample, Elliott Sober's forthcoming book Learning from Logical Positivism. we give up on logical empiricism. The problem, in some form or other, arises for nearly everyone. The aim ofthe logical empiricists was to develop a logical theory of ev­ idence and confirmation, a theory treating confirmation as an abstract re­ lation between sentences. It has become fairly clear that their approach to the problem is doomed. The way to analyze testing and evidence in science is to develop a different kind of theory. But it will take a lot of discussion, in this and later chapters, before the differences between apprc;>aches that will and will not work in this area can emerge. The present chapter will mostly look at how the problem of confirmation was tackled in the middle of the twentieth century. And that is a tale of woe. Before looking at twentieth-century work on these issues, we must again look further into the past. The confirmation oftheories is closely connected to another classic issue in philosophy: the problem ofinduction. What rea­ son do we have for expecting patterns observed in our past experience to hold also in the future? What justification do we have for using past obser­ vations as a basis for generalization about things we have not yet observed? The most famous discussions ofinduction were written by the eighteenth­ century Scottish empiricist David Hume ([1739] 1978). Hume asked, What reason do we have for thinking that the future will resemble the past? There 39 40 Chapter Three Induction and Confirmation 41 is no contradiction in supposing that the future could be totally unlike the directly described by the theory ofconfirmation, nonetheless scientific pro­ past. It is possible that the world could change radically at any point, ren­ cedures might be based on assumptions described in the theory of confir­ dering previous experience useless. How do we know this will not happen? mation. Perhaps scientists do many things that cannot be justified if con­ We might say to Hume that when we have relied on past experience before, firmation does not exist. this has turned out well for us. But Hume replies that this is begging the Let us look more closely at what the logical empiricists tried to do. First, question-presupposing what has to be shown. Induction has worked in I should say more about the distinction between deductive and inductive the past, sure, but that's the past! We have successfully used "past pasts" logic (a distinction introduced in chapter 2). Deductive logic is the well­ to tell us about "past futures;' But our problem is whether anything about understood and less controversial kind oflogic. It is a theory of patterns of the past gives us good information about what will happen tomorrow. argument that transmit truth with certainty. These arguments have the fea­ Hume concluded that we have no reason to expect the past to resemble ture that ifthe premises of the argument are true, the conclusion is guar­ the future. Hume was an "inductive skeptic;' He accepted that we all use anteed to be true. An argument of this kind is deductively valid. The most induction to make our way around the world. And he was not suggesting famous example of a logical argument is a deductively valid argument: that we stop doing so (even if we could). Induction is psychologically nat­ ural to us. Despite this, Hume thought it had no rational basis. Hume's in­ PREMISES All men are mortal. ductive skepticism has haunted empiricism ever since. The problem ofcon­ Socrates is a man. firmation is not the same as the classical problem of induction, but it is closely related. CONCLUSION Socrates is mortal. A deductively valid argument might have false premises. In that case the 3.2 Induction, Deduction, Confirmation, and Explanatory Inference conclusion might be false as well (although it also might not be). What you The logical empiricists tried to show how observational evidence could get out of a deductive argument depends on what you put in. provide support for a scientific theory. The idea of "support" is important The logical empiricists loved deductive logic, but they realized that it here; there was no attempt to show that scientifictheories could be proved. could not serve as a complete analysis ofevidence and argument in science. Error is always possible, but evidence can support one theory over another. Scientific theories do have to be logically consistent, but this is not the The cases that were to be covered by this analysis included the simplest whole story. Many inferences in science are not deductively valid and give and most traditional cases of induction: if we see a multitude of cases of no guarantee. But they still can be good inferences; they can still provide white swans, and no other colors, why does that give us reason to believe support for their conclusions. that all swans are white? But obviously not all cases of evidence in science For the logical empiricists, there is a reason why so much inference in are like this. The observational support for Copernicus's theory that the science is not deductive. As empiricists, they believed that all our evidence earth goes around the sun, or for Darwin's theory of evolution, seems to derives from observation. Observations are always of particular objects work very differently. Darwin did not observe a set of individual cases of and occurrences. But the logical empiricists thought that the great aim of evolution and then generalize. science is to discover and establish generalizations. Sometimes the aim was The logical empiricists wanted a theory of evidence, or "theory of con­ seen as describing "laws of nature;' but this concept was also regarded firmation;' that would cover all these cases. They were not trying to develop with some suspicion. The key idea was that science aims at formulating a recipe for confirming theories. Rather, the aim was to give an account of and testing generalizations, and these generalizations were seen as having the relationships between the statements that make up a scientific theory an infinite range of application. No finite number of observations can con­ and statements describing observations, which make the observations sup­ clusively establish a gerieralization of this kind, so these inferences from port the theory.