What If?

Thought Experimentation in Philosophy

Nicholas Rescher

• Publisher: Routledge
• Year: 2018
• ISBN:
  9781351321860
• Edition: 1
• Topic: Philosophy
• Subtopic: Philosophy History & Theory

Thought experimentation has been a staple of philosophical methodology since classical antiquity, when Xenophanes of Colophon speculated that if horses had gods, they would be equine in form. Nicholas Rescher's What If? undertakes a systematic survey of the role and utility of thought experiments in philosophy. After surveying the historical issues, Rescher examines the principles involved, and explains the conditions under which thought experimentation can validly yield instructive results in philosophy. The reader gains understanding of the differences between scientific and philosophical experiments.

What If? begins by examining the nature of thought experiments. It presents an overview of how thought experiments have figured in natural science and in historical studies, before moving on to examine how they function as an instrument of philosophical inquiry. After examining thought experiments from the pre-Socratics to the present day, Rescher turns from history to analysis, and examines the modes of reasoning involved in the use of speculative hypotheses in philosophical problem solving. He shows the limitations of speculative ontology, showing that thought experimentation can lead readily to paradox in a way that increasingly diminishes its usefulness. The book concludes by arguing and illustrating how and when it becomes pointless to push speculation, or thought experimentation beyond the limits of intelligibility and cogent sense.

Among the principal features of Rescher's book is its elaborate analysis of the appropriate conditions for philosophical thought experimentation. Its cardinal thesis is that there indeed are limits to the appropriateness of this important methodological resource and that transgressing these limits destroys the prospect of drawing any valid lessons for the philosophical enterprise. What If? will be of interest to philosophers, students of philosophy, and theorists of logic and reasoning.

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,¹ 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 on the whole as serviceable for handling our experiences mentally as those we actually use.²

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 versatility.³

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 conclusion 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 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 a question.⁵ Such reasoning is a matter of “thinking things through” 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, frictionless 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

• 2x = 3y
• x² − 1 = 0
• x + y = 5

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.

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 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 sevent...

Table of contents

• Cover Page
• Half title
• Title
• Copy right
• Contents
• Preface
• 1. Thought Experimentation
• 2. Thought Experimentation in Science and History
• 3. Thought Experimentation in Philosophy
• 4. Thought Experimentation in Pre-Socratic Philosophy
• 5. Some Classic Philosophical Thought Experiments
• 6. Aporetics and Cost-Benefit Analysis in Philosophical Thought Experimentation
• 7. Issues of Speculative Ontology
• 8. Philosophically Instructive Paradoxes
• 9. Outlandish Hypotheses and the Limits of Thought Experimentation
• 10. On Overdoing Thought Experimentation
• Bibliography
• Name Index