Change in View: Principles of Reasoning

'hange in View ' 'triples of Reasoning

Gill3ert Harman

A Bi-adford Book The MIT Press Cambridge, Massachusetts Loneion, England

0 1986 by The Massachusetts Institute of Technology All rights reserved. No part of this book may be reproduced in any form by any electronic or mechanical means (including photocopying, recording, or information storage and retrieval) without permission in writing from the publisher. This book was set in Palatino by The MIT Press Computergraphics Department and printed and bound by Halliday Lithograph in the United States of America. Library of Congress Cataloging-in-Publication Data Harman, Gilbert. Change in view. "A Bradford book." Bibliography: p. Includes indexes. 1. Reasoning. 2. Logic. 3. Belief and doubt I. Title. BC177.H37 1986 160 85-18766 ISBN 0-262-08155-5

Contents

Yr Intuitions? 40 What about 01 Keeping Track of Justifications 41 41 Clutter Avoidan c e Again Chapter 5 43 Implicit Comrnitments More on Positi v e Undermining 43 Reliability Conimitment 44 Likelihood 45 Conservatism: Tentative versus Full Acceptance Full Acceptanc e Ends Inquiry 47 W h y Full Acce,ptance? 49 Acceptance for Oneself and for Others 50 Conclusion !5 2

Contents

Acknowledgments

ix

Chapter 1 A Plea for the Study of Reasoning

1 Reasoning as Reasoned Change in View 1 Reasoning Distinguished from Argument or Proof Induction and Deduction 4 Descriptive versus Normative Theories 7 Human versus Artificial Reasoning 9 Summary 10

Chapter 6 Some Principliss of Belief Revision 55 The Relevance of Interests 55 The Interest in Not Being Inconsistent 56 The Get Back I-'rinciple 5 7 Measuring Min imal Changes 59 Long-Term vers;US Momentary Acceptance 61 Simplicity 611 Summary 63

3

Chapter 2 Logic and Reasoning 11 Implication, Inconsistency, and Practical Limits 11 Explicit and Implicit Belief 13 Clutter Avoidance 15 15 Unavoidable Inconsistency and the Liar Paradox 17 Immediate Implication and Immediate Inconsistency Summary and Conclusion 19

Chapter 7 Explanatory C