About Rationally Speaking

Rationally Speaking is a blog maintained by Prof. Massimo Pigliucci, a philosopher at the City University of New York. The blog reflects the Enlightenment figure Marquis de Condorcet's idea of what a public intellectual (yes, we know, that's such a bad word) ought to be: someone who devotes himself to "the tracking down of prejudices in the hiding places where priests, the schools, the government, and all long-established institutions had gathered and protected them." You're welcome. Please notice that the contents of this blog can be reprinted under the standard Creative Commons license.

Friday, June 11, 2010

Podcast Teaser: what about thought experiments?

Our next podcast will tackle the topic of thought experiments, in both science and philosophy. Philosophers are often accused of engaging in armchair speculation, as far removed from reality as possible, inside the proverbial ivory tower. The quintessential example of this practice is the thought experiment, which many scientists sneer at precisely because it doesn’t require one to get one’s hands dirty. And yet scientists have often engaged in thought experiments, some of which have marked major advances in our understanding of the world. Just consider the famous example of Galileo’s thought experiment demonstrating (rather counterintuitively) that two objects of different weight must fall at the same speed. (Contrary to popular belief, Galileo never actually climbed the leaning tower of Pisa to do this experiment – he didn’t need to.) Galileo knew that Aristotle would have predicted that a heavy body (H) would fall faster than a lighter one (L). But, the Italian scientist reckoned, suppose we connect the two bodies by a string, thereby making the compound object H+L. Following Aristotelian physics, one would predict that H+L should fall faster than H by itself because of the compound weight: therefore H+L > H. However, it’s also possible to use the same logic to claim that the compound body should fall at a slower pace than H because of the drag created by L, so that H+L reductio ad absurdum – that really H = L = H+L. As we know, Apollo 15 astronaut David Scott showed to the world that Galileo was right in a rather spectacular fashion. Such is the predictive power of thought experiments!
Then again, readers of this blog know the pretty low opinion I have of philosopher David Chalmers' famous thought experiment about zombies and the so-called "hard problem" of consciousness. Chalmers says that he can conceive of zombies that act and behave and talk like us, and yet have no consciousness. From that he deduces a form of dualism in which consciousness does not have to be tied to a particular physical substrate. As I pointed out in my earlier post, however, conceivability is not a reliable guide to possibility. I can conceive of impossible things, such as the idea of squaring the circle, or of a god that is omnipotent and yet can make a mountain so big that she couldn’t move it, and so on. Chalmers comes up with an (admittedly ingenious) little story, and we are supposed to deduce from it the momentous conclusion that there is more than matter/energy to the universe? When things appear to be too good to be true, there is often good reason to think that they in fact are too good to be true. That is, Chalmers' thought experiment is bunk.
Still, there are plenty of good thought experiments in philosophy, beginning with the so-called trolley dilemmas meant to probe our moral intuitions. I wrote about those too on Rationally Speaking, concluding that the more I read about trolley problems the more I am intrigued by the possibility that some of our moral intuitions may not be rationally defensible, setting up an interesting area of inquiry about the relative importance of reason and emotions in ethics.


  1. Doesn't the efficacy of a thought experiment depend on how well the experimenter can extrapolate from previous experience? And aren't all experiments, hands on or not, based in part on extrapolation from subjective experience?

  2. Massimo,

    Maybe it's a simplistic issue but I have trouble understanding this idea of "conceiving of" something (like in "conceiving of zombies" or a "maximally perfect being"). It seems to me that most of the time when we believe we can conceive of something we are simply fooling ourself: we have an image of an object or a scene in which we can use the term in a seemingly meaningful manner but in fact we have no precise idea at all of what we are talking about. If this is the case then arguments assuming that we can conceive of something don't seem to amount to much.

  3. I don't think our moral intuition or any other intuition is rationally defensible. Surely that isn't a controversial position. Intuitions are shortcuts past explicit reason. As such they can be useful even when formally wrong.

    We experience moral choice and so reify it as a thing out there. We even experience it as a sense of presence and worship it as a god.

  4. Massimo:

    Thou definitely doth protest too much about Chalmers (references in 4-5 posts in one year?), so can only assume you to be an admirer of the man's work.

    It may be your opinion that conceivability does not imply possibility, but it was not backed up with convincing arguments in the Anything is Possible... thread that for some reason turned into a chat about the existence of a god or gods, and get hung up on 'Cantor problems' that muddy the waters by introducing godly omnipotence into these questions.

    It is not only Chalmers thinking the world is made of more than matter and energy. Wheeler, Lloyd and others have been quite clear how and why this simply cannot be true, and so it is useful to think of the world as information, although the theoretical basis for applications beyond the quantum realm has not been firmly established. But it needs to be said over and over again that these people are scientists reviewing scientific questions, and this is why one person's nonsense is another person's reality.

    JP: One's idea can be considered every bit as real as a rock that was tripped over while thinking about the idea. While this was not always true, we now have no basis for thinking otherwise, because it makes more sense to view all real things as images

    Everything around you is perceived as images or subjective conceptions. and less useful to divide the world ideas and images on one side and 'real stuff' on the other.

    My view of the rock is not yours, neither of them being a nonexistent 'precise idea' of the thing, as you would have it.

    These ideas are not new. I see that Berkeley's 18thC definition of Immaterialism was refuted with e act of one Samuel Johnson kicking his shoe into a rock. To which I can only say the guy kicked a rock, and it became front and center in his mind. But for those of us who did not know about this story, the rock did not exist, all historical record to the contrary.

  5. Regarding Galileo and falling bodies, he wasn't the first individual to think in this fashion. Benedetti was before Galileo and rejected Aristotle's ideas for falling bodies under very similar grounds. He came up with a slightly different but incorrect hypothesis for falling bodies where the denser a body the faster it falls. In fact, to distinguish between Benedetti and Galileo you need more than this thought experiment and need to do some form of actual experimentation (such as with pendulums).

    DaveS, that's inane. If things we don't know about didn't exist then we'd never have unexpected discoveries. Moreover, if in order to defend P-Zombies you need to move to some form of extreme monism then the entire point of the idea fails.

  6. Before anyone here derides thought experiments as not being "real" science, let's not forget a certain scientist who only ever engaged in thought experiments: Albert Einstein.

  7. I can conceive of robots that act and behave and talk like us, and yet have no consciousness.
    Suppose we have a very good mathematical model of the brain, and we simulate it on a simple but extremely fast computer. It'll behave like a brain, but it won't be conscious since all it does is perform one arithmetic operation at a time.

    The trolley dilemma is rationally defensible. The collateral damage scenario does not use the passerby to stop the trolley, but the murder scenario does use the passerby.

    It's hard to articulate intuition because by definition it's stuff we know without having to think about it. Some of it is instinctive, and the rest is learned through practice.

  8. What about thought experiments in ECONOMICS?

    Double-entry accounting is 700 years old. How hard can it be? What if accounting had been mandatory in our schools since 1960? What would the NET WORTH of the average American be today? How many Americans today can't explain what NET WORTH is?

    Does the way our economy works depend on keeping most people ignorant?

    Economic Wargames

  9. The trolley experiments seem to point out to an unconscious mechanism making the moral judgment. While these (certainly evolved) mechanisms are good enough to produce adequate actions in most real situations, the artificial constraints of the experiment induce this "moral sense" to make a seemingly irrational decision. This is similar in a way to how astutely constructed drawings can produce visual illusions. Should we talk of moral illusions in this and similar cases? In any case I tend to think that moral judgments are mostly intuitive and rationalization mostly after the fact.

    Maybe the "trolley effect" may help explain why the so-called collateral damages in wars are generally seen as acceptable.

  10. If consequentialists think that the two trolley scenarios are equivalent, and murder is as acceptable as collateral damage, that makes me scared of consequentialists. After they push the fat guy off the bridge, would they also steal his wallet and cut out his organs to save some more people?

  11. I have been playing with the thought experiment recently that moral intuitions are actually society conditioned reflexes. Society being defined as an extended face group of people that think and act like those in the "respected" face group.

    This of course could be a religious group, but for a secular person the social group is selected from among the various social groups available, neighbors, work groups, avocational groups, university alumni groups etc. Particularly for those who move among many groups it is imperative and quite natural to learn and respect if not always comply with the social conditioning from each group.

    Family and family mentors are the first and most important social reflex conditioning group and family conditioning is always dominant although modifiable particularly with the teen rebellion and regrouping that takes place then.

    The trolley dilemma makes more sense as the pushee is implicitly part of the social group and protection and respect for all in the social group is if not instinctual one of the most powerful of the social conditioned reflexes. The people on the tracks are simply outsiders some of which will not survive.

  12. Max,

    The deliberate intervening into a situation that one is not part of, flipping a switch to cause the trolley to kill an individual that was in no danger prior to your action, is unimportantly different than the pushing of the fat man. Your wanting to call one "murder" and the other not does not make sense to me.

    If you flip the switch on purpose, like you do in the first case, but there are not 5 passengers on board that train, then that would clearly be murder, right? Only because you believe you have "just" cause in flipping the switch, with five people on board, do you mitigate your action as "collateral damge" and not murder. But the same "just" cause mitigation can be used for pushing the fat man.


    I agree that social conditioning plays a major factor in many of our moral intuitions, but instinct and genetic structures are also clearly mixed in there too. Joshua Greene and others have focused on studies showing that the emotional feelings associated with pushing someone, like in the trolley case, (an emotion that is very instinctual, I would say) affects our intuition about the morality of that action. I think it is grossly overboard to say that all our intuitions come from non-social emotions and reactions, but they clearly play large roles.

  13. I was listening to the Philosophy Bites podcast and an ethicist made the point, and I agree, that these trolley thought experiments are not really a healthy way to think about morality. It's literally dehumanizing to imagine these scenarios, and, short of stressing the brain for the sake of fMRI scans, there is very little practical value to this. They really aren't that informative or revealing. Can you tell me something useful that's come from these fantasy killings? People feel an innate repulsion to one type of expedient killing but not another. Really? How useful is this knowledge? Would you rather cut off a baby's head or a dog's head? Yuck? The question repulses you? Then why should you feel okay about contemplating these other deaths? I'm inclined to (blast from the past) Carol Gilligan's critique of this type of "morality." Fun for the philosophers but corrosive to the soul.

  14. My rule of thumb is that the branches of philosophy where thought experiments still flourish are, by no accident, the most impoverished. Ethics, Philosophy of Mind. Massimo was right to take Chalmers (not to be confused with A.F. Chalmers who wrote "What Is This Thing Called Science?") to task. Einstein's gedanken experiments were much more clear, cautious and fruitful, because at the end of the metaphor, a physicist has to produce an equation. At the end of his thought experiments, Chalmers only needs to put on his leather coat and drive of on his motorcycle.

  15. Lyndon

    I find the social conditioning very difficult to separate out as for so many years the social group was the village or the church, frequently essentially the same thing. But looking at the modern reality of multiple social groups to "choose from" I am seeing powerful moral influences that may differ substantially from the traditional go along to get along moral paradigm.

  16. @OneDayMore:
    Michael Faraday didn't produce any electromagnetism equations; he left that to James Clark Maxwell.

  17. Good point Kimpatsu, but if it weren't for Maxwell's equations (which were the reason I dropped out of Physics, btw) then you wouldn't know Faraday's name just as you don't know the names of the dudes who came up with caloric and phlogiston. And that's the difference between physics and philosophy. There are still Platonists but not Ptolemists. And for the same reason, annoying thought experiments like "Mary's Room" and Chalmers' zombies will be manuring PhD's for years to come. All you need is a clever metaphor and a clever "conceive of" (as JP points out) and you don't have to worry about some Maxwell coming along and trying to clean up your finger paint. Man I wish I had been able to grock those equations. Maybe if I had faked my way through...

  18. @OneDayMore

    You mention the critical view of "trolley" experiments by an ethicist. Here's another way to look at this.

    There is strong evidence that at least a large part of our moral judgments are made in an intuitive or automatic manner. Massimo reaches a similar conclusion at the end of another of is posts (he links to it at the end of this one). For want of a better term, let's call this our "moral subsystem". The question now is: how can we study this? How do we find out how it works? We cannot just think about it or dissect the brain or whatever. We need some reliable way to probe its internal mechanisms. One approach (of which the trolley story is an example, not all of them involve killing) is to design situations involving a moral choice and determine how people react to it (that is, you provide some well controlled input to the moral subsystem and observe what happens). These situations are by necessity artificial because of the complete control you need, in particular to make the experiment reproducible with different "subjects" and to eliminate external factors (noise) that might affect the decision. Repeating the experiment with a small variation (as in the trolley story) is, of course, a way to measure the importance of a single factor.

    I agree that the thought experiment in itself may not be that interesting. It becomes so when you do actual experiments with real people. There is a lot you can study this way, not the least being the influence of culture on moral decisions. Presumably, decisions that are the same in all cultures are more likely to be under biological control than others. This is not something you can know without rigorously testing it.

    As I am not familiar with the field (I have read about this, but it's been a while) I don't really know how much success has been achieved (or not), or how important this research is. But, overall, this approach makes sense to me. It is certainly worthwhile to try it at least until we can determine whether it can produce significant results or not.

  19. Also, to the extent that I understand Faraday (not at all), he was devising models more than thought experiments.

    But, let's consider the qualitative difference between Einstein's trolley thought experiment (wasn't he on a trolley?): "What would it look like if this trolley were going the speed of light?" The only out of bounds questions that I can think of are trivial and not directly related to the conclusions he wants to draw--How could you go the speed of light? That's all I can even think of.

    Now think about a morality trolley thought experiment: the trolley has x number of people who will die if you don't kill y people in z way. But what if I yelled down to the guys on the track? OUT OF BOUNDS! What type of people are x and y? OUT OF BOUNDS! What if I sacrifice myself? OUT OF BOUNDS! But these questions are not really out of bounds. These are the actual types of considerations one would have in making a real world decision of this sort. So contrived. I wonder if this isn't really a meta experiment in rationalizing murder.

  20. OneDayMore,
    > People feel an innate repulsion to one type of expedient killing but not another. Really? How useful is this knowledge?

    It's useful to know which intuitions are innate and which are culturally conditioned, and which parts of our brains are involved.

    My intuition about the first scenario is that the group of people are in the same position as the single person: tied to a track, and the fact that the trolley heads toward the group seems like either bad luck or planned by the evil mastermind who tied everyone down. Well why should I let dumb luck or an evil mastermind select the worse outcome, when I can select the better outcome?

    The second scenario asks whether murder for a good cause is justifiable. If it is, then I'm in immediate danger, since my organs and property could probably save several lives.

  21. @Max

    I guess, but I’m just not sure there isn’t something else going on here. Trolley Problems are “fun” in a way that I think isn’t about ethics. I would want these dehumanizing fantasies to yield a lot before I would feel justified in this sort of mind game. Let me put it this way...

    Imagine a trolley whose track was set up in such a way that all the passengers would suffer incest unless you throw a switch by having an incestuous relationship with your own child. What would you do?

    Now, this thought experiment is more contrived than most, but not by much. In fact, this thought experiment is, in terms of potential insight, every bit as valid as any other. Yet I’m sure you feel a certain revulsion in imagining this scenario. You probably question my motives in devising it. You probably wonder about my character. Now it is incumbent on you to explain what exactly is the difference between my thought experiment and yours.


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