What If? Thought Experimentation in Philosophy 2005043713, 0765802929, 9780765802927

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What If?

What If? Thought Experimentation in Philosophy

Nicholas Rescher

First published 2005 by Transaction Publishers Published 2017 by Routledge 2 Park Square, Milton Park, Abingdon, Oxon OX14 4RN 711 Third Avenue, New York, NY 10017, USA

Routledge is an imprint of the Taylor & Francis Group, an informa business Copyright© 2005 by Taylor & Francis. All rights reserved. No part of this book may be reprinted or reproduced or utilised in any form or by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying and recording, or in any information storage or retrieval system, without permission in writing from the publishers. Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation without intent to infringe.

Library of Congress Catalog Number: 2005043713 Library of Congress Cataloging-in-Publication Data Rescher, Nicholas. What if? : thought experimentation in philosophy/ Nicholas Rescher. p.cm Includes bibliographical references (p.) and index. ISBN 0-7658-0292-9 (alk. paper) 1. Thought experiments. I. Title. BD265.R47 2005 101-dc22 2005043713 ISBN 13: 978-0-7658-0292-7 (pbk)

Contents

Preface 1. Thought Experimentation 1. Suppositions 2. Thought Experimentation 3. The Need for Context 4. Logical Aspects 5. Uses of Thought Experiments 6. Problems of Subjectivity 7. Malfunction in Thought Experimentation

2. Thought Experimentation in Science and History 1. Scientific Thought Experiments 2. Historical Thought Experiments 3. Thought Experimentation in Philosophy 1. Philosophical Thought Experiments 2. Typification vs. Counterexampling 3. A Philosophical Tool 4. Analogy and Burden of Proof

4. Thought Experimentation in Pre-Socratic Philosophy 1. Thales of Miletus 2. Anaximander of Miletus 3. The Pythagoreans 4. Xenophanes of Colophon 5. Heraclitus of Ephesus 6. Coda

5. Some Classic Philosophical Thought Experiments 1. Life is but a Dream (Plato's Dreamer) 2. Plato and the Ring of Gyges 3. Buridan's Ass 4. Descartes' Deceiver 5. Descartes' Wax 6. Locke's Locked Room 7. Locke's Changelings 8. Leibniz's Mill 9. Peirce's Stone 10. James' Squirrel 1 1. Chisholm's Changeling 12. The Prisoner's Dilemma 13. Some Lessons 6. Aporetics and Cost-Benefit Analysis in Philosophical Thought Experimentation 1. Counterfactuals 2. Validating Counterfactuals 3. The Weakest Link in Philosophical Aporetics 4. Aporetic Clusters in Philosophy 5. The Determinative Role of Systematicity Considerations 7. Issues of Speculative Ontology 1. The Difference between Actual and Merely Suppositional Objects and States of Affairs 2. How Fictional Possibilities Differ from Real Things 3. Impossible Objects 8. Philosophically Instructive Paradoxes 1. Paradoxes 2. The Liar and His Cousins 3. Russell's Paradox 4. Goodman's GruelBleen Paradox 5. The Role of Distinctions 6. Reductio ad absurdum 7. Thomson's Lamp as an Illustration of Reductio Reasoning 8. Per Impossible Reasoning

9. Outlandish Hypotheses and the Limits of Thought Experimentation 1. Far-Fetched Hypotheses and Diminishing Returns 2. Meaninglessness 3. Suppositions that Go Too Far: Limits of Meaningfulness 4. How Outlandish Hypotheses Pose Problems 5. Use and Usage 6. The Shipwreck of Conjectural Analysis in Philosophy

10.

On Overdoing Thought Experimentation 1. Two Worlds 2. Different Priorities 3. A Fuzzy Boundary 4. Reality Respect Endangered Bibliography Name Index

1 Thought Experimentation 1. Suppositions Philosophers have often said things to the effect that people whose experience of the world is substantially different from our own are bound to conceive of it in very different ways-and thereby operate in terms of very different category-schemes. Supporting considerations for this position have been advanced from very different points of view. One example is a thought experiment suggested by Georg Simmel in the last century-that of envisaging an entirely different sort of cognitive being,' intelligent and actively inquiring creatures (animals, say, or beings from outer space) whose experiential modes are quite different from our own. Their senses respond rather differently to physical parameters-relatively insensitive, say, to heat and light, but substantially sensitized to various electromagnetic phenomena. Such intelligent creatures, Simmel held, could plausibly be supposed to operate within a largely different framework of empirical concepts and categories-the events and objects of the world of their experience would doubtless be very different from our own. The way in which they describe the realm of their experience might differ radically. In a similar vein, William James wrote: Were we lobsters, or bees, it might be that our organization would have led to our using quite different modes from these [actual ones] of apprehending our experiences. It might be too (we cannot dogmatically deny this) that such categories, unimaginable by us to-day, would have proved

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What If?

on the whole as serviceable for handling our experiences mentally as those we actually use.' Different cultures and different intellectual traditions, to say nothing of different sorts of creatures, will, so it has been widely contended, describe and explain their experience-their world as they conceive it-in terms of concepts and categories of understanding substantially different from ours. They may, accordingly, be said to operate with different conceptual schemes, with different conceptual tools used to "make sense" of experience-to characterize, describe, and explain the items that figure in the world as they view it. And it is clear that the substantiation of any such conclusion will crucially and unavoidably rest on thought experimentation. In intellectual regards, homo sapiens is an amphibian who lives and functions in two very different realms-the domain of actual fact, which we can investigate in observational inquiry, and the domain of imaginative projection which we can explore only in thought by means of reasoning. This second ability becomes crucially important for the first as well, when once one presses beyond the level of a mere description of the real to concern ourselves also with its explanation. In the history of Western thought, this transition was first made by the Greek nature-philosophers of pre-Socratic times. It is they-as will be seen-who invented thought experimentation as a cognitive procedure and practiced it with great dedication and ~ersatility.~ To us moderns, brought up on imaginative children's nursery rhymes ("If wishes were horses, then beggars would ride") exposed to manifold fictions, this sort of belief-suspensive thinking seems altogether natural. But it takes a competent logician to appreciate how complex and sophisticated thought experimentation actually is. What it involves is not simply drawing an appropriate conchsion from a putative fact; rather, it exploits the higher-level consideration that a particular thesis (be it fact or mere supposition) carries a certain conclusion in its wake. Supposition is, of course, a commonplace device that operates via such familiar locutions as "suppose," "assume," "what if," "let it be that," "consider the hypothesis that," and the like. A supposition is not an acknowledged fact, but a thesis that is accepted "provisionally" or laid down "for the time being." A mere supposition must, as such, be deemed if not false, then at least uncertain to some extent; if it were deemed true there would be nothing assumptive about it.4 It is the

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occurrence among the premisses of an argument of such a suppositional hypothesis that renders such a piece of reasoning in which it figures a "hypothetical." Supposing something to be the case is conceptually more sophisticated than affirming it to be the case. The person who does not grasp what it is to accept the claim that p is in no position to suppose doing so, even as the person who imagines finding a dollar bill must know what actually finding a dollar bill would be like. From the logical point of view, knowing is supposing. For consider: One can only know so what is actually true, which is obviously not so with supposing. And one can suppose something in one context of discussion, and something else that is incompatible with it in another whereas knowledge is once and for all. Supposing is conceptually more complex than knowing.

2. Thought Experimentation A "thought experiment" always rests on suppositions. It is an effort at drawing instruction from a process of hypothetical reasoning that proceeds by eliciting the consequences of some projected supposition which, for aught that one actually knows to the contrary, may well be false. Such a process consists in reasoning from a supposition that is not accepted as true, and perhaps is even known to be false, but is assumed provisionally in the interests of making a point or answering ~ reasoning is a matter of "thinking things through" a q ~ e s t i o n .Such with regard to the larger implications and ramifications of the proposition being supposed. And with suppositions, two sorts of situations can arise. The supposition that inaugurates a thought experiment may well supplement the body of already available information by extending it into a region that was previously terra incognita. However, it also may, alternatively, abrogate our information by way of dismissal, replacing at least a part of it with something that is contradictory to it. Thought experiments of the former agnostic (belief-supplemental) type are comparatively conservative, while those of the latter (belief-conflicting) type are more radical in nature. Indeed, thought experiments can go beyond this to be based on assumptions that are viewed not imply as false but as actually impossible. And this happens even with scientific thought experiments such as those which stipulate things like perfectly elastic bodies, perfectly homogeneous objects, friction-

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What If?

less surfaces, absolute vacuums, ideal market economies, social contracts, and the like. Overall, then, thought experiments fall into two principal categories. In the first instance there is: the agnostic where we simply do not know whether or not the supposition in question is true or false. ("If that was indeed John, then he [John] was not born in 1920.") Here it is perfectly possible that the defining supposition is realized and the antecedent of that conditional true: one just doesn't know, and as far as the experiment is concerned, it just doesn't matter.

Agnostic thought experiments are perfectly genuine experiments. The assumptions on which they pivot will involve purely speculative scenarios that nowise conflict with any belief to the contrary. A hired assassin bursts into the room. With one blast of his powerful shotgun he renders his immobile victim to smithereens. But unbeknownst to him, this individual has just expired, killed by the poison his disaffected brother slipped into his lunch. Legally, that assassin is innocent of murder: in law one cannot murder a corpse. But surely the issue of moral guilt remains open. Clearly-so our lesson runs-the questions of legal and moral culpability represent quite different issues. So what we have here is a cogent and instructive thought experiment, albeit one that involves no recourse to counterfactuality. However, thought experimentation is often based on suppositions that are more "far out" than what such "agnostic" scenarios involve. And so another important category of thought experiments is: the disbelieved (or belief-contravening) where we actually accept something that conflicts with the supposition in question. ("If Hannibal were alive today, he would use tanks and not elephants.")

And an important subcategory of the latter is The fanciful where one fully realizes that the supposition is utterly impossible. ("If 4 were a prime, there could be five prime numbers between 2 and 12.")

The question around which it revolves is crucial to a thought experiment. Thus consider the following situation: Suppose that the following three pieces of information are given regarding two otherwise unspecified real numbers x and y

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Now if the question is: "What are the values of x and y?" the thought experiment must be deemed impracticable. There simply are no qualities x and y for which these conditions are feasible. On the other hand, if the question is "Will there be such numbers or are the specified conditions unrealizable?" then the thought experiment is altogether successful and simply issues in a negative answer. In theory, there is no limiting the nature of the supposition at issue. Supposing is a pretty open-ended process. In The House at Pooh Corner, Piglet anxiously asked: "Suppose a tree fell down, Pooh, when we were underneath it?" With unaccustomed acuity, Pooh replied: Supposing it didn't." Anything that can be talked about can be the subject of suppositions. But while a thought experiment will pivot on a supposition, it will have to be one that is specifically designed to facilitate the solution of a motivating problem. After all, we can suppose "for the sake of discussion" or "for the sake of illustration" and so on. But only when a supposition is made for the sake of instruction-for setting some larger, more far-reaching issue-is a thought experiment at hand. A thought experiment is thus by nature a combination of a supposition combined with a question; it is characterized by a supposition designed to resolve some larger issue. Thus suppose people gave up on luxury, ostentation, and frivolity, and matters of "conspicuous consumption" in general. The resulting collapse of economic activity might well lead to economic depression and general impoverishment-so picturesquely argued Sir Bernard Mandeville's Fable of the Bees. And the wider lesson he drew was that whatever defense of rustic simplicity and abstemious virtue there might be, its utilitarian support in terms of general advantage to the standard of living and material well-being will not be available. (In this regard thought experimentation resembles real experimentation.) And so not any and every hypothesis or assumption is a thought experiment. For example, consider Let us suppose a windowless room that is bare except for a chair positioned in the middle of it.

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What If?

There is as yet no thought experiment at issue here. For there is no indication of the point of the exercise-no indication of any larger lesson. Only when that is supplied will the case afford us a thought experiment. There is thus an important difference between thought experimentation and mere speculation as such. "What if one could converse with flowers?" "What if I could project myself back to the time of Julius Caesar?" "What if one could change base materials into Gold through a 'Midas touch'?'These are interesting questions that invite enlivening speculating. But they do not constitute thought experiments unless and until one specifies some larger problematic issue whose solution such speculation is able to facilitate. Suppose that someone writes a word beginning with A. And suppose someone then comes along and erases that A. What can we conclude about the remaining inscription? The answer is: very little indeed. If indeed anything is left it need not be an English word. Nor can we say anything whatever about what its initial (or last) letter is. Nothing whatever can be concluded. But still there is a lesson here, viz. that thought experiments can be perfectly practicable and meaningful without their launching suppositions themselves yielding any substantively germane conclusions. And there is another lesson as well. Suppositions can occur within suppositions. Just as statements can involve further statements and questions further questions, so suppositions can involve further suppositions. We can suppose a group of people who are aware that there are five of them in the room. And we can then go on to suppose that one of them supposes two of - the others to be absent. However, this is tantamount to supposing that one of five people in a room, all of whom are aware of there being five, one supposes that two of the others are missing. Multiple suppositions can always be compounded into single ones. However, one and the same thought experimental supposition can yield very different results. Thus suppose that telekinesis were possible. We might go on from this to draw conclusions about the engineering of mind-matter interactive devices. Or we might go on to draw conclusions about the rule of mind in nature's scheme of things. The taxonomic nature of a thought experiment (as practical say or philosophical) does not so much hinge on the thematic nature of its launching supposition as on the nature of the lesson we propose to draw from it. What if Anglo-American orthography abandoned capital letters and

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proceeded in the manner of e. e. cummings? Think of the enormous savings of time and effort in writing and printing. Surely on-paper communication would be just as intelligible-after all, we do not differentiate capitalized words in speech. All this is true enough. But nevertheless there is no thought experiment here until such time as a larger lesson of some sort is indicated-perhaps relating to the extent to which man is a creature of habit. Thought experiments often invite us to suppose a situation which could in fact be realized if one wished to take the time and trouble. It is simply convenience and economy of effort that leads us to thought experimentation here. We could actually carry out the experiment at issue but there is no real point to it-the whole lesson to be learned here can just as readily be secured on the basis of supposition pure and simple. But many thought experiments cannot be carried out at all. Some rewrite history ("How would seventeenth-century philosophy have developed if Descartes had died at childbirth), some turn on suppositions that are unachievable in principle. ("Suppose the diagonal of a square commensurable with its sides"), some are physically unrealizable ("Suppose you were moving with a ray of light at its own speed"), etc. Thought experiments need not be "contemplations in thought as to how an experiment would actually work out" because they are, often as not, dealing with nonexperiments-procedures that cannot possibly be carried out at all. They are not a matter of thinking about experiments, but are, rather, experiments in thinking. A thought experiment need not be an imagined experiment because when the conditions being supposed are unrealizable in principle it will not be possible for an actual experiment to be carried out. On this basis, thought experiments are complex courses of hypothetical reasoning. They set out from a supposition, supplementing it with a (generally tacit) group of facilitating premises. And they then move on to establish a conclusion by standard (generally deductive) reasoning. Moreover, they go through this process in order to answer some experiment-characterizing questions-not because the conclusion affords an answer (which it cannot do because its basis is merely suppositional), but rather because that question is resolved by the conditional fact that that particular supposition succeeds in underwriting that particular c o n c l ~ s i o n . ~ Effectively by definition, then, a thought experiment will have to include: (1) the supposition that it projects; (2) the context of informa-

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What If?

tion into which this supposition is being introduced; (3) the conclusi~n that is then derivable by means of this supposition; (4) the larger question it is designed to answer (i.e., the lesson that is drawn from it); and ( 5 ) the course of reasoning through which the preceding considerations are to be seen as providing the grounds for the purposed answer/lesson. Accordingly, we can say that thought experimentation involves five stages overall: supposition, context-specification, conclusion-deriving, lesson drawing, and synoptic reasoning. And it is crucial to note here that the "result" of a thought experiment is not that conclusion itself, but rather the lesson that results from the fact that a supposition-underwritten conclusion follows from the governing supposition in the context of guiding beliefs. Thus take that thought experiment about the flying pigs. The supposition that sets its stage is "Pigs can fly." The supplementing information includes such beliefs as that creatures will, on suitable occasions, exercise the capabilities they have. The conclusion that is derived is "Pigs will sometimes fly." And the lesson we now propose to draw is: "Not every thought experiment is all that interesting." And the course of reasoning through which this lesson is drawn is a matter of viewing this thought experiment as itself providing an instructive example of this very lesson. An actual experiment, if experiment it is, will have an actual outcome of some sort. A thought experiment, by contrast, will generally have not one outcome but a range of possible outcomes. And the upshot of conducting a thought experiment need not lie in the actual realization of one or another of these possible outcomes but a recognition that some are more plausible-more powerfully indicated-than others. Actual experimentation is an exercise in the observation of nature, thought experimentation is an exercise in rational reflectionin assessing the contextual plausibility of reaching a certain conclusion in the circumstances created by stipulative conditions. A thought experiment is no more an experiment than a plastic flamingo is a flamingo. There may be various points of resemblance, but there is no kinship. It is not, however, strictly speaking, the case that thought experiments proceed by thought alone and use no equipment or instrumentations. Architects may build models to shape their plans, war planners may use miniature tanks or battleships in table exercises, physicists or astronomers may use computers to carry out their thought experiments. But all of these different ways of simulating reality by use of artifacts

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afford ways of thought experimentation exactly because we are here dealing with a symbolically thought-controlled surrogate for reality and not with the relevant sector of reality itself.

3. The Need for Context Suppositional reasoning will only rarely and counterfactual reasoning never can proceed in an informational vacuum. And throughout thought experimentation there is recourse to key aspects of the prevailing state of relevant fact to provide the stage setting for the reference that we draw (in general deductively) from the informative situation opened to view by our governing supposition. In many cases, our suppositions may prove insufficient for meaningful thought experimentation able to yield definite conclusions. Consider an example: Would the predictability of human actions spell an end to free will? Suppose that X could reliably predict all of Y's choices. Would this put paid to Y s freedom of choice? It all depends. To address the issue we would have to flesh out more fully the still missing gaps of the scenario. For the crucial question arises of just how it is that X arrives at those predictions. Thus if X makes those predictions through his knowledge of the causal consequences of presently detectable conditions then we enter into a realm of causal determinism which would, arguably, render Y' s chooses unfree. But, on the other hand, should it be that X somehow has a (doubtless mysterious) pre-cognitive insight into the future-possibly due to some (doubtless mysterious) backwards causation-then there is nothing about his precognition that would render those future choices of Y s in any way unfree. The crucial point here is that how thought experimental suppositions work out will generally depends on considerations relating to a context larger than anything is made apparent in the experiment-projecting supposition itself. Consider the following set-up as a given:

And now contemplate a conditional of the format If there were no x in that box, then -.

There is effectively nothing that we can plausibly fill into that blank short of trivially. ("Then there would be no x in that box"). There is

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What If?

simply too little context. The crucial question as the where we can possibly go from here is left unaddressed. One might, to be sure, be tempted to endorse the consequences. then there would be one less x on the page. But is this really so? With a bit more context along the lines of "because that x is now erased away7' or "because that x is now shifted an inch to the right" the tenability of the counterfactual would become settled one way or another. With more context we come to be in a position to say something more definite. But without sufficient context, there is nothing further that we can say. For thought experiments are only meaningful within a larger context of information. Thus suppose that some cigarette smoke were released in a confined perfect vacuum. Would it eventually diffuse homogeneously? This question is not easily resolved-and cannot in fact be settled conclusively by actual experimentation-"perfect" is too difficult and "eventually" too long. But in any case it is a question one cannot meaningfully address (let alone resolve!) without a great deal of physics at one's disposal. Contextual information is thus essential for thought experimentation. Consider the classic thought experiment devised by Galileo to refute Aristotle's theory that heavier objects fall faster than lighter ones. On such a theory, Galileo asked, what is to happen when a heavier object falls while being pinned to a lighter one. Then the composite object H & L must (by the theory) fall faster than H alone since it is obviously heavier. But since L alone will fall more slowly than H, joining the slower L to H must retard the speed of H's fall. To dispel such inconsistency, objects must fall at equal speeds, regardless of weight. So reasoned Galileo. But of course this argumentation presupposed many unspoken beliefs, including the ideas that conjoining does not transform the holistic nature of an object, making it a "big bully" that can push its way along more rapidly. And without the supplemental assumption that a compound object behaves as a single unit, the thought experiment will not be able to do its work. (And of course this assumption itself carries the main burden of the earlier "experiment.") In general, the more reliance a thought experiment places on the background of information relevant to its formative suppositions, the more informative it is. When the conclusion follows logically from the supposition itself the thought experiment is simply trivial. ("If there

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were fifty people in the room, then there would be more than forty people there" is totally true but thoroughly trivial. But, " then the floor would most likely collapse" is distinctly more newsworthy.) The exact composition of the set of environing beliefs is crucial for the sort of "conclusions" that can be drawn from a supposition. Thus if teacher X believes that Johnny is at bottom a pretty able student, while teacher B has a far lower opinion of Johnny's capabilities, then in confronting the claim "Johnny has the ability to learn how to do long division" it will transpire that X accepts this as true while Y rejects it as false. And of course their difference in this regard will lead them to opposite views regarding the acceptability of the counterfactual conditionals: If (only) Johnny had studied harder he would have passed the examination. (Even) if Johnny had studied harder he would not have passed the examination.

It is clear that in thought experimentation, as elsewhere, the conclusions we draw will depend on the premises we endorse. To be sure, the background of relevant information that is at issue would not always be clear and explicit: critical analysis may be requires to bring it into focus. But for fruitful thought experimentation it must invariably be there. Let it be that you find a (partly illegible) manuscript note reading: He sent her a I-tter.

..

You now confront the question: How is that missing gap to be filled in? It must be a vowel, so in theory it could be A, E, I, 0, or U, and you proceed to list these alternatives by supposition. Clearly the appropriate answer will depend on the context of relevant information that is available. If she has just been injured the answer may well be I. But if they are lovers separated through travel it would presumably be E. And here everything depends on just exactly what question is being asked. If the question is changed to "How can that missing gap be filled i n ? ' t h e answer is clearly: Either by I or by E. But if the question is "How must that missing letter be filled in," then there simply is no appropriate answer and the thought experiment must be seen as flawed.

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What If?

Of course, neither in science nor elsewhere do thought experiments create substantive information ex nihilo. Consider some illustrations. In Newton's spinning bucket experiment, what is deduced by way of conclusion is that the surface of the water will assume a concave shape owing to the action of centrifugal force. But the ultimate lesson of the thought experiment is something quite different, viz. that-since there are no other objects for the bucket to relate to-the operation of physical forces proceeds in relation to an absolute (object-independent) space. Categorical results cannot be extracted from mere suppositions. Whenever thought experiments succeed in yielding factually informative conclusions from suppositions-mere hypotheses-it is not and cannot be on the basis of such assumptions alone but involves an at least tacit recourse to a penumbra of peripheral fact or belief. With respect to physics, this very point has been urged eloquently by John Norton: Thought experimentation in physics provides or purports to provide us information about the physical world. Since they are thought experiments rather than physical experiments, this information does not come from the reporting of new empirical data. Thus there is only one non-controversial source from which this information can come: it is elicited from information we already have by an identifiable argument, although that argument might not be laid out in detail in the statements of the thought experiment. The alternative to this view is to suppose that thought experiments provide some new and even mysterious rout to knowledge of the physical world.'

However, while thought experimentation certainly cannot establish matters of contingent fact, what it certainly can do is to demonstrate matters of logico-conceptual possibility. For such possibility is a matter of coherence and consistency-which is to say a matter of reasoning which, after all, is what thought experimentation is all about. One recent author on thought experimentation characterizes the pro~ it is clear in the light of the cess as one of "armchair i n q ~ i r y . "But preceding considerations that this is not quite fair. For while thought experimentation is indeed a matter of calculation and reasoning, nevertheless the materials providing input into this process-the premises from which it proceeds and upon whose substance it is predicatedare bound to come form our inquiries at large and neither need nor generally will issue from the armchair.

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The larger lesson involved in a thought experiment does not lie in the substances of the consequences that follow from its launching suppositions, but rather in the wider ramifications of the higher-level circumstances that, given the wider cognitive context at issue, those consequences ensue from the supposition. Again, consider, for example, the counterfactual supposition that we had no capacity for foresight and prediction. It would then follow that we could not engage in anticipation and planning-that the future consequences and implications of our actions were something wholly outside our ken. Relative to this consequence, there emerges the larger lesson that moral responsibility for our acts-sorr;'ething for which a realization of their impact upon other persons and situations is in general crucial-is crucially dependent upon foresight, so that predictive foresight into the ramifications and consequences of action should be seen as a crucial precondition for morality. Theorists disagree about the nature of the background of belief that affords a thought experiment's stage setting. Some theorists think that it reflects our mental model of real it^,^ possibly one that is imprinted ~ look to an instinctive intellectual in our thought by e v o l ~ t i o n . 'Others insight into a realm of natural necessity.I1 Still others look to a body of historically developed awareness of theses that characterize fundamentals of scientific practice.I2 The best plan, however, is to see that informative background of supposition-correlative beliefs as a manifold of information that is available to us in the problem-context before us.13 Accordingly, the "inference" at issue is simply a matter of reasoning deductively from a supposition in conjunction with a (generally tacit) family of background belief. Thought experiments are certainly not a means for gaining instructive insight into a special domain of otherwise inaccessible truth about substantively factud matters. The mainstream tradition of Western epistemology insists emphatically that abstract thought and reflection alone cannot provide information about factual matters and insists that thought cannot extract facts ex nihilo. But some theorists deny this and insist that thought experiments provide a counterexample to the idea that pure thought is informatively impotent in relation to matters of worldly fact. Some of these theorists insist that evolution has imprinted into our minds a capacity for insight into nature's ways in a way that thought experimentation can bring to the fore.I4 Other theorists insist that empiricist inclinations cannot account for the ability of

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What If?

thought experiments to provide insight into the laws of nature somehow constituting a distinctive realm of Platonic forms.I5 But of course such developmentally grounded inclinations cannot establish facts; they can at best indicate presumptions.I6 The circumstance that they figure in thought experiments that we deem as somehow instructive and illuminating does not change their epistemic status into something else by transmuting presumptions into facts. Those necessary background assumptions needed for a thought experiment to work out are and remain just exactly that-background assumptions based on conjectures and perceptions. They represent not deeper insight into a remote realm of experimentally inaccessible fact but rather experimentally grounded conjectures and presumptions which, in the end, may or may not prove to be sustainable.

4. Logical Aspects One theorist characterizes thought experiments as "experiments performed in the laboratory of the mind."I7 And it may seem only natural to characterize a thought experiment as some sort of actual experiment, specifically one that "purports to achieve its aim without the benefit of execution" as another theorist suggest^.'^ But this is very problematic. For actual experimentation addresses a question to nature in circumstances where the experiment would be pointless if there were no uncertainty as to what the outcome will be. By contrast, thought experimentation addresses a question to the body of inform ation in hand and is fruitless unless this body is already in a position to render some particular outcome a foregone conclusion through reasoning alone. Thought experiments are not, in fact, "performed" any place-unlike real experiments they are not performances but courses of reasoning from a set of suppositions. If by way of a thought experiment we institute the supposition S and then on its basis claim the conclusion C to be somehow warranted, just what sort of warrant can be at issue? How can we get insight into warranting relationships after we step outside the realm of fact and reality into that of mere supposition? We must of course immediately acknowledge that what we now have is not C as such, but rather C's following from S (in the context of our background information B). But following in what sense? Thought experimentation is an exercise in reasoning, and reasoning

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requires a functioning logic. But what of such a logic itself? Is it sacrosanct? Can we not undertake thought experimentation that calls even this-even logic itself-into question? Gottlob Frege certainly thought so: But what if beings were even found whose laws of thought flatly contradicted ours and therefore frequently led to contrary results in practice? The psychological logician could only acknowledge the fact and say simply: those laws hold for them, these laws hold for us. I should say: we have here a hitherto unknown type of madness. Anyone who understands laws of logic to be laws that prescribe the way in which one ought to think-to be laws of truth, and not natural laws of human beings' taking a thing to be true-will ask, who is right? But whose laws of taking-to-be-true are in accord with the laws of truth?. . . The impossibility of our rejecting a logical law hinders is not at all in supposing beings who do reject it; where it hinders us is in supposing that these beings are right in so doing, it hinders us in having doubts whether we or they are right.lY

And here the result of Frege's thought experiment-that the supposition that logic should be replaced by something else, something different, something discordant from it-is in effect a reductio ad absurdurn. We must accept logic as we know it as a given.

5. Uses of Thought Experiments One way of classifying thought experiments is by the thematic subject matter of that what if question: is it scientific in mathematical, legal or philosophical, or what? For example, "What if people lived on would the laws of taxation and the average of 200 years-how pension for social security funding have to be revised?' is clearly a question of political economy constituted to the thought experiment of the supposition at issue. And thought experiments designed to answer the question "Would it be a goodlbad thing if people were more candid with one another?'would belong to the realm of social ethics. Thought experiments can also be classified by the nature of the reasoning process leading from the supposition to the derived conclusion (e.g., is it deductive or probabilistic or plausibilistic). Then too, thought experiments can be divided into those used constructively for substantiation and those used destructively for refut a t i ~ n .For ~ ~instance, the generalization that generous acts betoken

16

What If?

virtuous character in the agent can be refuted by the thought experiment of supposing some monstrous malefactor-a Hitler, say, or a Stalin-moved to some acts of generosity by a yearning for public praise. Or again the thesis that good intentions mitigate the evil of wrongdoing might be substantiated by a thought experiment that projects some typical sort of transgression (lying, say) which needlessly emerges from a thoroughly praiseworthy (such as safeguarding the potential victim of an enraged maniac). Thus, if in supposing a condition of type A you are constrained (in the interest of coherence and consistency) to reject and exclude B, then you establish a negative result to the effect that "A's cannot be B's." And of course in the special instance of the latter case when A = B, then you establish that "A's cannot be A's" or-in effect-that A's are impossible. Here, then, you have a reductio ad absurdum that constitutes a refutation of the A's as such. One useful and very common use of thought experimentation relates to its explanatory employment. We here reason along the lines of "If only such-and-such were the case, then something-or-other (which otherwise would be very difficult to explain) now admits of a ready and satisfying explanation." For example, Thales, the very first of the nature philosophers of ancient Greece, proposed to explain the annual flooding of the Nile as the result of the backing up of its outflow due to the opposing force of the annually recurrent Etesian winds. Again, Charles Darwin gave thought experimentation a prominent place in his overall reasoning: In order to make it clear how, I believe, natural selection acts, I must beg permission to give one or two imaginary illustrations. Let us take the case of a wolf, which preys on various animals, securing some by craft, some by strength, some by fleetness; and let us suppose that the fleetest prey, a deer for instance, had from any change in the country increased in numbers, or that other prey had decreased in numbers, during the season of the year when the wolf is hardest pressed for food. I can under such circumstances see no reason to doubt that the swiftest and slimmest wolves would have the best chance of surviving, and so be preserved or selected. [For] . . . some of its young would probably inherit the same habits or structure, and by the repetition of this process, a new variety might be formed which would either supplant or coexist with the parent-form of wolf.21

Just as natural science has no monopoly on experimentation properwhich can, of course, be conducted in such everyday affairs as

Thought Experimentation

17

cookery or instructional management-so it has no monopoly on though experimentation either. In a way, even a mere analogy or metaphor can encapsulate a thought experiment. Take, for example, the Biblical analogy of the wifelmother to a fruitful vine. Here the following thought experiment is implicitly at work in addressing the question: "What role does the wifelmother play in the scheme of things?" Suppose that we think of the wifetmother as a fruitful vine. We will then understand better and more clearly her-role in the scheme of things. For just as the vine bears fruit so she bears her children, and just as the vine supports its fruit and keeps its fruit safe so does she with her children, and just as the vine brings nourishment to its fruit so doe she with her children.

As this example indicates, many thought experiments are not all that interesting. Thus consider "If pigs could fly, they sometimes would" which envisions the thought experiment of flying pigs and answers the question "What are some of the things that will happen in these circumstances?" In thought experimentation, as elsewhere, one can reason about trivial issues as well as significant ones. Often the merit of a thought experiment lies precisely in the economy and convenience it affords in rendering an actual experiment unnecessary. This is particularly evident when thought experiments are used in the context of planning. T h u s consider, for example, an architect who contemplates how high to position the entry floor of a building. If too low it may flood; if too high it will be inconvenient for access. He needs "to think through" the consequences of the various alternatives in advance and by such thought experimentation seeks to avoid the expense and possible misfortune that a real experiment could well involve.

6. Problems of Subjectivity As an exercise is abstract reasoning, thought experimentation falls outside the purview of psychology. One recent writer speaks of "the currently popular view that thought experimentation is best understood in connection with the notion of mental models."22 But, popular or not, this idea is very questionable. Thought experiments sometimes involve the construction of models (as in architecture) and sometimes even of mental models (as in the

18

What If?

use of differential equations to represent physical processes). But some theorists go so far as to view thought experimentation in general as a matter of mental modeling. But this is a mistake. There is no need for modeling in thought experimentation: what is at issue is merely the explanation of consequences ensuing upon the introduction of an assumption into a context of beliefs. Thought experiments certainly need not-and often do not-deal with mental models or constructs or images or anything merely mental. They address hypothesis-engendered results that yield instruction through working out the accommodations and readjustments that have to be made to realize some coherent and consistent group of overall suppositions. They are in sum exercises not in model construction or imaginative design but in processing information in rational inquiry. After all, in typical thought experimentation the question is not (or need not be): What would I (be inclined to) say if But rather: What would-and

indeed should-one

say if -

In general, the crux of thought experimentation is not a matter of subjective inclination or personal response, for the point at issue generally is-and should be-as generic, impersonal, and objective as any other. Thought experimentation is, to reemphasize, an exercise not in introspection but in reasoning. Thought experimentation requires imagination in its pliance on the supposition of unknown conditions. And it requires reasoning because it requires one to figure out what follows-"what is to be said7'-in the circumstances. Moreover it requires evaluation because while there are already different-and generally discordant-things than can be said, they will differ in point of plausibility and the object of the exercise is precisely to identify the optimal, maximally plausible alternative. Nevertheless, the process is an objective matter of dealing with the realities of the situation. The cogency of thought experimentation is contextual but not subjective-it depends on the available information but not on the personal attitudes or inclinations of the experimenters. The upshot of a cogent thought experiment will pivot on establishing a thesis on the order of "If such-and-such were the case, one would be rationally

Thought Experimentation

19

well-advised to maintain p (rather than Q or anything else). And such thought experimentation is not an exercise in subjectivity. Its orientation is not psychological: it does not address what you or I or any other particular individual is inclined to say or feel or do. The key issue in addressing these "What i f ' questions is not "What am I tempted or inclined to assert in these conditions?" but rather "What would it make good sense to assert in these condition^?"^^ Rather, its concern is normative and impersonal, asking what should be said or done, what is the proper and appropriate response. One of the tasks that can conveniently be accomplished by thought experiments-indeed one that is seen by some writers as their principal objective-is a matter of checking introspectively one's natural, intuitively inclinational response towards a particular h y p ~ t h e s i s . ~ ~ This might be characterized as the "What would you say i f . . . ?" use of thought experimental suppositions. This is not, however, a very satisfactory account. For one thing, it makes thought experimentation an exercise in introspective subjectivity-something which it ought not to be and for which it can now be rescued only by the problematic postulation of a "modal interaction" that offers quasi-objection insight into the inner possibilities of things. And for another thing it overlooks the fact that thought experimentation-like real experimentation-is not a matter of idle curiosity but serves a larger function, that of providing a means for helping to settle a more deep-rooted and farreaching question of some sort. A supposition projected merely for the casual contemplation of intriguing possibilities is a matter of idle speculation rather than thought experimentation. Repeated assertions to the contrary notwithstanding, thought experimentation need have nothing to do with i n t r o ~ p e c t i o n .To ~ ~be sure, there can indeed be thought experiments that are explicitly introspective: "If a lion came into the room what would you think/say/do?" But other, even closely related thought experiments will have nothing introspective about them: "If a lion came into the room what should you do?" (Answer: leave rapidly and call the zoo for help.) There is nothing introspective here. It is fundamentally a matter of what it would be sensible for you-or indeed anybody-to do in the circumstance. And it is also necessary to realize that the "should" at issue here is the epistemic rather than the moral should. Consider the thought experiment of being confronted with a cluster of green marbles and

20

What If?

asked, "What is the color of those marbles?'Clearly one should-on moral grounds of candor and honesty reply, "Green." But this consideration of moral propriety is not at issue in thought experimentation, where that specified answer should be given simply because it is correct, because it conveys true information rather than mis-information, because it squares with the facts of the case. The case is, different, to be sure, where specifically autobiographical thought experiments are involved. Again consider the following thought experiment: "Suppose I were to wake up tomorrow without any recollections regarding anyone whom I did not know at the age of twenty. How would I respond?" Clearly if I am the sort of individual to whom personal relationships matter greatly, I might well return to the scene of my youth and try to pick up the threads with people I still know. On the other hand, if I am the sort of person whose thoughts dwell in the realms of generality (as a pure mathematician, say) then I might prefer simply to carry on as before. In ways such as these, thought experimentation can be a useful instrument in self-insight and self-understanding. Here introspection will be our guide. But of course this is not something that lies in the nature of thought experimentation in general. It is the result simply of the fact that this particular thought experiment poses a specifically introspective question about one in particular. If the thought experiment were altered to be generic and the question changed to "How should one respond?" we would be in a situation of informational insufficiency. Too much hinges on the otherwise unspecified aspects of the situation. One can, of course, undertake to examine one's epistemic inclinations via an introspective assessment of one's belief reactions in conjectural matters. But such excuses in subjective self-examination have little bearing on thought experimentation at large. For here the aim of the enterprise is the quest for cogent answers to questions, and the pivotal issue is not that of "What am I inclined to think?" but rather "What is it that people should think because in the circumstances this is the appropriate and most cogent thing to think-that for which there are the best and strongest reasons." Proper thought experimentation is an exercise in objective rationality.

Thought Experimentation

21

7. Malfunction in Thought Experimentation Thought experimentation is exempt from all sorts of misfortunes and malfunctions that can cause failure in actual experimentation: flawed apparatus, careless observations, environmental disturbances, and so on. Such misfortunes, inherent in operations in the physical world, are spared to the thought experimenter, whose mishaps are confined to the realm of deliberation which, of course, has its own panoply of pitfalls by way of the errors of omission and commission that can arise throughout our intellectual ventures. As we have seen, a thought experiment involves five stages overall: supposition, context specification, commitment adjustment, conclusion deriving, and lesson drawing. And at each of these stages a mishap or malfunction can in theory arise. The supposition can turn out to be meaningless. The context may be set up inappropriately, in relation to the purposes of the thought experiment in particular by way of error of omission. The commitment adjustment may fail to be realistic, in particular by way of errors of omission that plunge matters into inconsistency. The course of reasoning by which the intended conclusion is drawn may be flawed and erroneous. The wrong lesson can be drawn for the experiment by overlooking possibilities for its interpretation.

In sum, all sorts of procedural flaws can, in theory, arise to vitiate a thought experiment. And, in fact, one of the most common failings of thought experiments is that they prove inconclusive owing to insufficiencies in their specification. Take the biologist's hypothesis: "Suppose a species of organism that has no predators at all. What sorts of factors might then limit its population?" But what sort of organism is it-is it animal or vegetable or humanoid? Everything is left up in the air. For whenever we draw out the implications of a supposition we must do so in the context of the relevant information of its cognitive envisionment. And in complex situations this context may speak with forked tongue through acknowledging conflicting tendencies. Thus suppose people generally told each other the unvarnished truth. Would we have then a utopia of trust and knowing where we stood? Or would there be a hell of mutual antagonism and rancor? A pretty good case could be made out either way.

22

What If?

The reality of it is that thought experiments will generally have to bear the responsibility for their own failure. In particular, thought experiments can fail: 1. From lack of information needed for bringing the launching supposition of the thought experiment into a decisive contact with the problem being addressed. (Flaw of information insufficiency.) 2. From mistakes in reasoning process that leads from the leading supposition of the thought experiment to a resolution of the public being discussed. (Flaw of reasoning.) 3. From hitting the wrong target, so to speak, in drawing the wrong lesson from the thought experiment in relation to the question being addressed.26

The inherently controversial nature in this regard is illustrated by Isaac Newton's famous hypothetical Spinning Bucket. Here centrifugal force leads the water level to rise towards the edges. But when this happens altogether in vacuo-where the basket is surrounded by nothing but empty space-there is nothing external for the basket to relate to-its space is absolute, relative to nothing save the (envisioning) space itself. But since the phenomenon is real so also is absolute space. So resolved Newton. But Ernst Mach flatly denied these contextual contentions. In vacuo, he insisted, the surface of the water would stay flat as a pancake. And in reality-when the experiment is conducted in the physical world-there indeed is something relative for determining the bucket's envirming space, namely the manifold of the stars set throughout the heavens.27 Can honest people perform dishonest acts? Some might suggest the following thought experiment Suppose X entrust a sum of money to Y. X has an identical twin brother Z who reclaims the money. Y , being honest, gives it "back." But in this giving that entrusted money to any person Y has done a dishonest act.

Seeing this thought experiment seemingly provides affirmative response to our question. But appearances are misleading. The indicated conclusion does not follow. All that follows is that Y has performed a mistaken or erroneous act, but not a dishonest one. Dishonestly would occur only if that wrongful transfer were willing and deliberate. As it

Thought Experimentation

23

stands, the thought experiment has failed to realize its objective through being based on an erroneous premise. One highly important class of "what if' questions is constituted by predictive issues relating to future possibilities. What would you do if your house burned down? How would Anglo-Canadians respond if Quebec split off into independence?

The difficulty with thought experiments of this sort lies in the problems affecting the contextual information required for the establishment of any sort of cogent conclusion. People's self-insight is very limited-they generally do not "know themselves" well enough to achieve secure foresight into hypothetical situations. And much the same holds for our insight into the make-up of others required for securely predicting their responses. Moreover our contemplation of future eventuations always leaves out of sight the vast amount of detail that characterizes any actual course of development. (For example, that initial question leaves out of sight the issue of whether that fire was caused by lightning or by the malicious vandalism of an antagonistic neighbor.) In such predictive cases the absence or indefiniteness of requisite information will all too often render a thought experiment too indefinite and "speculative" for profitable contemplat i ~ n . ~ ~ As such examples show, one key problem for thought experimentation lies in the possible insufficiency of circumambient information. For the assumption at issue can prove to be under-informative and unable in and of itself to resolve the question being posed. Assume a one-windowed room. Such suppositional stipulations merely create an oasis of putative fact within a desert of unanswerable questions. What color are the walls in the room? Where is it located? What is the chair made of? At what distance are the legs of the chair from the walls of the room? Our stipulations float free in a vacuum of missing fact. Those questions indicate missing facts of the matter. Walls-real walls-will have to be of some color or other. But that's just it, those presently contemplated walls aren't real. To ask for the color of that hypothetical wall is like asking for Sherlock Holmes' shoe size. There is no answer here-no fact of the matter-because the question runs outside the scope of the issue-defining supposition^.^^

In an intriguing discussion of farfetched assumptions in ethics P. H. Nowell-Smith poses the question "What would you say if you added a column of ten figures one hundred times and got one answer fifty times and another fifty times?" His response is: "1 simply do not know what 1 should say, for the logic of my language for talking about . . . adding does not allow for this sort of thing."30 But this is not really the best reaction. For the supposition in question here is simply too vague. It leaves too much unsaid. We need to know the details. Am I arithmetically challenged and incompetent? Am 1 fixated on 222 and will offer this as one response (among others) to any arithmetical problem. Am 1 optically weird and will at times persistently read 8 as 3? That "What will you say i f ' supposition is simply too indefinite-too lacking in detail-to make a sensible response possible. The problem does not lie in the farfetchedness as such of the supposition, but in its lack of informative One major way in which a thought experiment can fail occurs when its launching supposition is under-informative in relation to the question being posed. This situation is standard in belief-contravening (or counterfactual) situations. The classic example is that of the question: If Bizet and Verdi were fellow countrymen what nationality would Bizet be? The problem of course is that that counterfactual hypothesis can be realized in very different ways, namely by allowing Bizet's nationality to be that of Verdi's or conversely allowing Verdi's to that of Bizet. And the supposition itself is underinformative with respect to this question-decisive issue. Exactly this sort of thing is at issue with a supposition on the order of X's exchanging memories with Y . The exact process through which X's acquisition of Y s memories is going to be central whether it be by hypno-suggestion and brainwashing, for example, or by Pavlovian conditioning or by "magic." The "outcome" of that thought experiment will very much depend on filling out the incomplete data of its inadequate projection. Thus in calling into question our standard practice of personal identification by assigning an individual name, Ludwig Wittgenstein wrote: Imagine, for example, that all human bodies which exist looked [exactly] alike. . . . [Then]it might be useful to give name to the sets o f characteristics [ofindividuals], and the use o f these names would now roughly correspond to the personal names on our present language.32

But this thought experiment is quite problematic. How could its

Thought Experimentation

25

supposition possibly be fleshed out to make sense? Would there no longer be observable differences between the bodies of men and women, or infants and septuagenarians, of athletes and housebound valetudinarians, and anorexics and gourmands? And even if, per impossible, these ceased to be observable differences between humans, what sorts of characteristics are now to be at issue for differentiation? Physical comportment (brow furrowing or chin stroking), sub-observable physical differences (fingerprints), ways of speaking (voice pattern identification)? Or perhaps people are simply given a serial number at birth-much as artists number prints-and these tattooed on their arms (in the manner of Nazi concentration camps). The point is that Wittgenstein's supposition is totally indefinite and undeterminative. All we could say in the sketchy circumstances at issue is that (1) we would still need to use some way of identifying individuals, and (2) that this would be different from the physical appearance ("mug-shot") manner in current operation. What this would likely be-say, whether by means of sets of descriptive characteristics of some particular sortis something that one simply cannot say in the insufficiently specified conditions. Of course the reverse situation-that of an informational overdetermination can also occur. For consider the situation where it is supposed that Smith was born in 1898, Jones is eight years older than Smith, and Smith was fifteen when World War I ended (in 1918). How old was Jones when World War I broke out (in 1914)? The suppositional situation given here is actually overdeterminative: too much for consistency. Again, no answer to the question being posed can here be secured. Sometimes it may not be altogether clear exactly what the point of a thought experiment is. This occurs, in particular, when the question that a thought experiment sets out to address is so indefinite that it is hard to say just what the point of the exercise is. Thus consider such a speculative what-if thought experiment on the order of Suppose intelligent life existed on other planets and entered into electromagnetic communication with us. How would this affect us humans in regard to our self-image as "the crown of creation"?

Thought experiments are often used for consequence-exploration in matters of choice. The man who concluded "I could well be happy

26

What If?

with either, were t'other sweet charmer away7' has doubtless done some thought experimentation. Thought experimentation is a crucial resource for planning of every kind. Thus if shooting him with my bow and arrow is indeed the best plan for killing Cock Robin, I must compare it in thought with such alternatives as blowing him up with dynamite. But obviously I cannot make an experimental test both ways to see what works out best. All in all, then, thought experimentation can involve various sorts of error. Thought experiments can err by relying on background information that is misinformation. They can involve errors of reasoning to arrive at conclusions that do not actually follow from the premises they use. They can address questions that rest on flawed presuppositions, can fall short precisely because they are suppositions projected with a view to answering questions and resolving problems. And so, thought experiments can fail-just as real experiments can. They can do so by failing to provide cogently an answer to the question they are designed to resolve. Or else they can provide the right answer to the wrong question. A widely discussed philosophical thought experiment was projected by Hilary Putnam in 1975. It envisions a "twin earth" where a earthbound individual (Adam) had his physically indistinguishable identical twin (Twadam). Both of them use the word "water" and apply it to items that are phenomenologically indistinguishable. But on earth water is applied to H 2 0 while on twin earth, whose elements are constituted somewhat differently (albeit in ways lying between the threshold of casual observation), what is there called "water7' is actually HP20-. It now results that while the term used by Adam and Twadam have a different "meaning" (because they apply to different sorts of substance) nevertheless everything that figures in the thought processes of our trans-universal twins is exactly the same. And so, Putnam concludes, "meanings just ain't in the head."33 But it is very much open to question whether Putnam's thought experiment sustains his conclusion. For there are-or certainly seem to be-two quite different sorts of "meaning," namely referential meaning (which pivots on what a term actually applies to) and conceptual meaning (which pivots on the way in which the users of a term propose to understand it in their thought and discourse). Both we and Anixmander of Miletus use our (linguistically coordinate) term for the moon in just the same way. But conceptually we take a very different

Thought Experimentation

27

view of the matter, since he took the moon to be a hole in the comic framework through which we see the all-enveloping fire beyond. And although referential meaning is an objective matter that is not in anybody's individual head-or any particular culture's collective head, for that matter-this is emphatically not the case with conceptual meaning. And so, while the salient suppositions of Putnam's thought experiment certainly does support a point, it just is not exactly his point.

Notes 1. Georg Simmel, "Ueber eine Beziehung der Selektionslehre zur Erkenntnistheorie," Archiv fur systematische Philosophie und Soziologie, vol. 1 (1895), pp. 34-45 (see 40-1). 2. Pragmatism (New York: Longmans Green, 1907), p. 171. The basic line of thought goes back to the ancient sceptics. Compare Sextus Empiricus, Outlines of Pyrrhonism, I, 54,59-60,97, et passim. 3. Chapter 4 will substantiate this contention in detail. 4. "Supposition on the part of the Creator would be ridiculous, for supposition implies doubt." (Alfred Guillaume [ed.], The 'Summa Philosophiae' of AlShahrastani [Oxford: Clarendon Press, 19341, p. 62 of the translation). As noted above, conditionals whose antecedents are seen as true-factual conditionals, that is-are generally formulated with since rather than if. 5. The term "thought experiment" is based on the German Gedainken-experiment introduced by Ernst Mach in his 1883 (see pp. 32-41 and 159-62) and 1897. (For references of this name and date format see the bibliography at the end of the book.) 6. In his 1991 and 1996, John Norton rightly stresses the inferential nature of thought experimentation. 7. Norton 1996. 8. Chapter 4 of Sorenson 1992 is entitled "The Wonder of Armchair Inquiry." 9. Nercessian 1992. 10. Peirce 1935-54, Sorensen 1992. 11. Brown 1991 and Kripke 19xy. 12. McCallister 1996. 13. Rescher, 2005b (=Conditionals). 14. See for example Ernest Mach, The Science of Mechanics, (3rd ed.), tr. by Thomas J. McCormack (Chicago: The Open Court Publishing Company, 1907). 15. See for example Brown (1986) and (1991). 16. See Rescher 2005a (=Presumptions). 17. Brown 1991, p. 1. 18. Sorenson 1992, p. 205. 19. Gottlob Frege, The Basic Laws of Arithmetic, trans by Montgomery Furth (Berkeley: University of California Press, 1967), pp. 14-15. 20. Compare Brown 1991, p. 34.

28

What If?

21. Charles Darwin, O n the Origin of Species: A Facsimile of the First Edition (Cambridge, MA.: Harvard University Press, 1964), pp. 176-77 (90-91). See further the detailed treatment of Lennox 199 1. 22. Haggqvist 1996, p. 17. 23. In chapter 2 of Sorenson 1992 there is an extensive discussion on the question "What is the origin of retrospection" that drives the process of thought experimentation, and worries "that 'thought experiment' is just a twentieth-century emphasis, for the currently reviled term 'introspection."' Such worries can and should be set aside by the realization that "interpretation" is simply not at issue here. 24. See, for example, Brown 1986 and Wilkes 1988. 25. Unger 1992 devotes the better part of a whole chapter to the matter. 26. For an informative discussion of how thought experiments in physics can go wrong see Allen I. Janis in Horowitz and Massey 199 1. 27. For further detail regarding Newton's bucket experiment see Laymon 1978 and 1991. 28. On these issues see the author's Predicting the Future (Albany: State University of New York Press, 1998). 29. See Gale 1991. 30. Ethics (Harmondsworth: Penguin Books, 1954), pp. 240-41. 31. The topic of farfetched thought experiments will be investigated in detail in chapter 9. 32. Ludwig Wittgenstein, The Blue and Brown Books (New York: Harper, 1958), pp. 61 -62. 33. See Putnam 1975.

Name Index Albert L. Stevens, 172 Anixmander of Miletus, 26,63-65 Archimedes, 29 Aristotle, 10, 29,61,63, 64,69, 72n2, 77,78,93n10, 129, 135n3 Arthur, Richard,l7 1 Atkinson, David, 171 Austin, J. L., 171 A vicenna, 48 Barker, Stephen, 136n7 Baumgarten, Alexander Gottlieb, 64 Bennett, Jonathan, 46n 15 Blackmore, John, 17 1 Brown, James R., 271111, 27n15, 27n17, 27n20,28n24,45nl, 45114,45116, 93n15, 171 Broyles, James, 17 1 Bunge, Mario, 171 Buridan, Jean, 77-79,93n8,93n9 Burnet, John, 67, 68,69,70, 72n5, 72n6, 72n7,72n8, 171 Calderon, 73 Camp, Joseph, I71 Cantor, Georg, 138 Camap, Rudolf, 158117 Casey, Edward S., 171 Cervantes, 115, 116 Chammah, Albert M., 175 Chisholm, Roderick, 87, 88, 93n21,97, 108nl, 108n5, 1.591110, 171 Clarke, Samuel, 145 Cole, David, 93n18, 171 Cowley, Robert, 171

Dancy, Jonathan, 60n7, 172 Danly, John R., 172 Darwin, Charles, 16, 28n21, 29, 33 Davidson, Donald, 117n3 De Morgan, Augustus, 172 Dennett, Daniel, 172 Descartes, RenC, 74,75, 79-81, 87,90, 93n3, 93nl1, 134, 146, 172 Dionysius, 68 Drake, Stillman, 172 Dresher, Melvin, 88 Duhem, Pierre, 93n9, 172 Einstein, Albert, 29, 172 Ellis, Joseph L., 165 Evans, Jonathan, St. B. T., 172 Fearon, J. D., 172 Ferguson, Niall, 172 Fermat, 136n15 Flood, Merlin, M., 88 Flores, Angel, 93n10 Fodor, Jerry, 159n17, 172 Forge, John, 172 Frankfurt, Harry, 93n13 Franklin, Allan, 172 Frege, Gottlob, 15, 27n19 Gale, Richard M., 28n29, 136n14, 172 Galilei, Galileo, 10,29,30,32, 129, 136n13, 172 Gardner, Martin, 172 Gendler, T. S., 136n13, 172 Gentner, Dedre, 172 Genz, Henning, 172

178

What If?

George, Rolf, 172 Gettier, Edmund, 53 Goldman, Alvin, 172 Gooding, David C., 172 Goodman, Nelson, 108n1, 108n5, 125127, 135n5, 136n7, 136n8, 173 Hacking, Ian, 173 Haggvist, Soren, 28n22,94n23, 117, 158n1, 158n2, 158n3, 173 Hahn, Hans, 33,34,45n9 Hansson, 108114, 108115 Harman, Gilbert, 155,173 Harre, Rom, 173 Heath, T. L., 136n 12 Hejjenoort, J. van, 135114 Hekataios, 69 Hempel, Carl G., 45n 12 Heraclitus of Ephesus, 67-71,72115 Hesiod, 69 Hiebert, Erwin, 173 Hippasus of Metapontum, 65,129 Hippolutus, 72n3 Hippon, 61 Hobbes, Thomas, 54 Holton, Gerald, 173 Horowitz, Tamara, 281126,45111, 171-76 Hull, David L., 173 Humphrys, Paul, 173 Irvine, Andrew D., 173 James, William, 1, 86-87, 93n20, 173 Janis, Allen 1 ., 28n26, 173 Janoff-Bulman, R., 173 Kant, Immanuel, 5 1,56, 82 Keynes, J. M., 114 Kirk, G. S., 61,63, 64,65,66, 67,68, 69,72n 1,72n2,72n3,72n4,72n5, 174 KoyrC, Alexandre, 45n6, 174 Kripke, Saul, 27n11 Kuhn, Thomas, 32,45nl,45n7,45n8, 174

Kyburg, Henry E., 136n7 Lakatos, Imre, 174 Laymon, Ronald, 281127, 174 Leibniz, G. W., 50, 73, 83-84, 87, 92n2, 93n2, 93n7,93n17, 118,145,146, 1.58115, 158116, 174 Lennox, James G., 28n21, 174 Levy, Isaac, 108115 Lewis, David, 46n15,46n16, 174 Locke, John, 81-83,93n12,93n14 Lucretius, 29,45113 Lyons, William, 174 Mach, Emst, 22, 27n5, 27n14, 29, 31, 33, 34,35,45n2,45n5, 45nl0,71, 931119, 174 Mackie, J. L., 155 MacLachlan, James, 174 Mandeville, Bernard, 5 Martensson, E., 461116 Massey, Gerald, 28n26,45n 1, 171-76 McAllister, James W., 174 McCallister, 27n 12 McCloskey, M., 174 Meinong, Alexius, 148 Mersenne, Marini, 134 Michalski, K., 93n8 Mill, John Stuart, 149 Miller, A. I., 174 Miscevic, Nenad, 175 Mohanty, J. N., 175 Morris, Edmund, 165 Myers, C. Mason, 175 Nercessian, Nancy, 27n9, 175 Newton, Isaac, 12,22, 28n27,29 Nietzsche, Friedrich, 56, 109n10 Nisbett, Richard, 175 Norton, John, 12, 27n6, 27n7, 175 Nowell-Smith, P. H., 24 Nozick, Robert, 175 Olsen, James M., 175 Parfit, Derek, 155, 159n16

Name Index 179 Peirce, Charles Sanders, 27n 10, 34, 57, 84-86,931119. 175 Plato, 58,73, 75,76, 92,92111, 93n4, 93115, 101. 167, 175 Poincart, Henri. 124 Popper, K. R. 175 Prantl, Carl von, 135113, 175 Priestly, Joseph, 33 Putnam, Hilary, 26, 27, 281133, 151-52, 159118 Pythagoras of Sarnos, 65,69 Quine, W. V., 155, 1.58117, 159n1.5 Quinton, Anthony, 92n2 Ranke, Leopold von, 27 Rapaport, Anatol, 175 Raven, J. E., 61,63,64, 65, 66,67, 68, 69,72n1,72n2,72n3,72n4, 174 Reagan, Ronald, 165 Rescher, Nicholas, 27n12,27n16,46n 17, 108113, 108n5, 119n4,175 Roese, Neal J., 175 Rorty, Richard, 154 Ross, Lee, 175 Routley, Richard, 9 1, 92, 94n24 Routley, Valerie, 91,92,94n3-4 Russell, Bertrand, 53, 122-25, 135n2, 135114. 175 Sainsbury, R. M., 176 Searle, John, 52, 53,60n1 Sextus Empiricus, 27n2 Shoemaker, Sydney, 155, 159nl1, 176

Simmel, George, 1, 27n 1 Socrates, 76,77, 101 Sorensen, Roy, 27n8,27n9,27n103 27n18,28n23,45nll, 60n2.60n6, 117, 136nl1, 158nl, 159nl4, 176 Spinoza, B. de, 102, 109118 Stalker, Douglas, 135n5, 136n10, 176 Stevin, Simon, 30 Stove, D. C., 176 Strawson, P. F., 117nl Thales of Miletus, 16, 61, 62, 63 Thomason, Sara G., 176 Thompson. James F., 13 1. 132, 1361114, 176 Thomson. Judith James, 53 Tsouras, Peter G., 46n14 Unger. Peter, 281125, 158111, 176 Urbaniec. Jacek. 176 Vaihinger, Hans, 176 Welles, Orson, 166 Whitehead, A. N., 135n4 Wiggins, David, 155 Wilkes, Katherine, 281124, 60118, 142, 158114, 159n Williams, Bernard, 83, 152, 159n9 Wittgenstein, Ludwig, 24, 25,281132, 158117 Wolff, Christian, 156, 157 Xenophanes of Colophon, 65-67,68,69, 72n4