RATIONALITY AND LOGIC ROBERT HANNA Rationality and Logic 05615_Prelims.qxd 05/03/06 2:24 AM Page i 05615_Prelims.qxd 05/03/06 2:24 AM Page ii Rationality and Logic Robert Hanna A Bradford Book The MIT Press Cambridge, Massachusetts London, England 05615_Prelims.qxd 05/03/06 2:24 AM Page iii © 2006 Massachusetts Institute of Technology All rights reserved. No part of this book may be reproduced in any form by any elec- tronic or mechanical means (including photocopying, recording, or information stor- age and retrieval) without permission in writing from the publisher. MIT Press books may be purchased at special quantity discounts for business or sales promotional use. For information, please email special_sales@mitpress.mit.edu or write to Special Sales Department, The MIT Press, 55 Hayward Street, Cambridge, MA 02142. This book was set in Sabon by SPI Publisher Services and was printed and bound in the United States of America. Library of Congress Cataloging-in-Publication Data Hanna, Robert, 1957–. Rationality and logic / Robert Hanna. p. cm. “A Bradford book.” Includes bibliographical references and index. ISBN 0-262-08349-3––ISBN 978-0-262-08349-2 (hc : alk. paper) 1. Logic. 2. Psychologism. 3. Reasoning (Psychology). I. Title. BC53.H36 2006 128'.33––dc22 2005058402 10987654321 05615_Prelims.qxd 05/03/06 2:24 AM Page iv To MTH and ETH Le coeur a ses raisons que la raison ne connâit point 05615_Prelims.qxd 05/03/06 2:24 AM Page v 05615_Prelims.qxd 05/03/06 2:24 AM Page vi Contents Preface and Acknowledgments ix Introduction xi 1 Psychologism Revisited 1 2 E pluribus unum 29 3 The Logocentric Predicament 53 4 Cognition, Language, and Logic 77 5 The Psychology of Reasoning 115 6 Our Knowledge of Logic 155 7 The Ethics of Logic 201 Notes 233 Bibliography 285 Index 309 05615_Prelims.qxd 05/03/06 2:24 AM Page vii 05615_Prelims.qxd 05/03/06 2:24 AM Page viii Preface and Acknowledgments This book is about human rationality, logic, and the connection between them. On my view, this connection is both constitutive and mutual. More precisely, I defend the broadly Kantian thesis that logic is the result of the constructive operations of an innate protological cognitive capacity that is necessarily shared by all rational human animals, and governed by categor- ically normative principles. Working out and writing up this idea has in- volved many extended visits to the domains of logical theory and cognitive psychology. But although I am a philosopher who by virtue of a deep inter- est in human rationality is also deeply interested in logic and cognition, I am neither a professional logician nor a professional cognitive psychologist. So I want to make it very clear in advance that I am drawing and relying even more heavily than is usual for philosophers on the theoretical expertise of others. I hope to make my contribution at the synoptic level of the Big Picture, and then turn this project back over to the specialists as a new and important joint research program. I am very grateful to the following people for conversations or correspon- dence on and around my topic: Sean Anderson, Luc Bovens, Nicholas Denyer, Christopher Green, Neil Manson, Arlo Murphy, Graham Oddie, Alex Oliver, Eric Olson, Onora O’Neill, James Russell, Peter Strawson, Evan Thompson, Dana Vanzanten, John Vejsada, and Jessica Wilson. Shards of the material were presented to appropriately and helpfully skeptical audiences in talks at Cambridge University; King’s College London; Trinity College Dublin; and York University, Canada. Several of the central arguments were first sketched or talked out during a visiting fellowship at Clare Hall, Cambridge, in Michaelmas term 1998. Institutionally speaking, the Social Sciences and Humanities Research Council of Canada and York University generously gave me research grants 05615_Prelims.qxd 05/03/06 2:24 AM Page ix [...]... when tokened in others.) The second basic distinction is beween (c) the meeting -the- minimalstandards sense of rationality, and (d) the meeting -the- maximal-or-idealstandards sense of rationality In the meeting -the- minimal-standards sense, rationality means either possessing a psychological capacity for rationality or meeting the well-formedness conditions for being a rational procedure of the relevant sort... necessary for rationality, and hence means nonrationality; whereas in the meeting-themaximal-or-ideal-standards sense, irrationality merely means falling short of perfect rationality The third and last basic distinction is between (e) the principled sense of rationality, (f) the holistic sense of rationality, and (g) the instrumental sense of rationality In the principled sense, rationality means the possession... call this claim the logic faculty thesis The logic faculty thesis draws explicitly but not uncritically on some ideas of Kant, Boole, Quine, Chomsky, and Fodor But what is logic? This question can mean two very different things The first is: what is the science of logic? And the second is: what is the nature of logic? The first is a question internal to the logical enterprise itself, whereas the second is... configured for the representation of logic In other words, logic is explanatorily and ontologically dependent on rational animals, but logical facts are not reducible to the natural facts The view expressed by (iii) is what I call the logic faculty thesis, which in turn is the first of two basic parts of the doctrine of logical cognitivism Given logical cognitivism, we can consistently reject logical psychologism... method, and collectively the basic constraint on all other sciences and on the acquisition and justification of all genuine knowledge In other words, nothing in the world falls outside the theoretical purview of the exact sciences (3) Physicalist metaphysics says that the physical facts strictly determine all the facts Let the term the physical facts’ stand for every fact in the world about the instantiation... metaphysical and epistemological reasons, he was interested fundamentally in general propositions and the logical import of general referring terms But, for expository convenience, we can also add to the Aristotelian notion of the syllogism the later Stoic interests in the logical behavior of truth-functional connectives (such as “not,” and, ” and “if then”) and the logical import of names, and derive... about the connection between rationality and logic, it follows that the nature of logic is significantly revealed to us by cognitive psychology Correspondingly, I call the overall view expressed by the conjunction of my two central claims logical cognitivism Logical cognitivism has two important and rather controversial consequences First, the philosophers must reopen their door and civilly invite the. .. basic distinctions, and orient my view in relation to them The first basic distinction is between (a) the mentalistic sense of rationality and (b) the procedural sense of rationality In the mentalistic sense, rationality is a complex psychological capacity for logical inference and insight, and also for practical deliberation and decision making By contrast, in the procedural sense, rationality is a complex... philosophical wisdom that the logical and the psychological are intrinsically incompatible In my opinion, the view that logic and psychology are fundamentally at odds with one another could not be more mistaken On the contrary, if I am correct there is an essential link between logic and psychology, despite the fact that logical psychologism is self-refuting and hence false This brings me back to the first central... the nature of logic, each in the form of a basic problem Chapter 1 deals with the problem of logical psychologism: what is the relation between the logical and the psychogical? Here I argue that logical psychologism is a species of scientific naturalism; that scientific naturalism about logic is false; and that logical cognitivism can effectively avoid both logical scientific naturalism and the equally . tokened in others.) The second basic distinction is beween (c) the meeting -the- minimal- standards sense of rationality, and (d) the meeting -the- maximal-or-ideal- standards sense of rationality. In the. follow from the others is an argument. The asserted sentences are the premises of the argument. The asserted sentence that is held to follow from the others is the conclusion of the argument. The fact. universal “protologic,” distinct in structure from all classical and nonclassical logical systems, that is used for the construction of all logical systems. I call this claim the logic faculty thesis. The logic