How Helpful Are Thought Experiments?

Exploring two “intuition-pumps”

Lizzie Bestow
Nov 27, 2020 · 11 min read
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Thought experiments have often been a contested subject in philosophical circles. Some swear by them — as a means of testing our intuitions — and others deride them as thinly-veiled attempts to push our thinking one way or the others.

At their best they question our most foundational beliefs. Daniel Dennett is famous for calling thought experiments “intuition pumps”; they help us think about why we have certain intuitions. Here, we’ll look at two thought experiments that might be a little different to those you’ve come across before.


In the ethical debate surrounding abortion, the main contenders vying for moral rights have traditionally been seen as a woman and her unborn foetus. There are those who consider the unborn foetus to have full moral rights as a person, and those who deny that the foetus has moral standing (either at all, or over and above the moral standing of the mother).

The former is known colloquially as pro-life, and the latter is known as pro-choice. But how can one side influence the other? Well, Judith Jarvis Thomson did, with a novel thought experiment.

Traditional debates have centred around the status of the foetus. Is the foetus a person, and should it be afforded the full moral status of an adult person?

Much of pro-life argument centres around the supposition that it is; that all life is sacred, or valuable, or important. Much of pro-choice literature centred around arguing that the foetus was not a person and that the person who is carrying the foetus has the final say over what happens to their body.

One philosopher, Judith Jarvis Thomson, sought to break with this pattern of back-and-forth. She could see that it was something of a moot point; both sides were talking past each other. They just could not agree. Thomson, instead, sought to argue that even if the pro-life supporters were correct, the carrier of the foetus would still have the final say. She argues that the fact that the foetus may be a person does not entail that the carrier has an obligation to keep the foetus alive.

Thompson begins her argument by stating that she will proceed as if both mother and foetus are fully moral persons, and thus frames the debate in the traditional conflict of rights. In her article, ‘A Defense of Abortion’, she uses a thought experiment in order to tests our intuitions around personhood:

You wake up in the morning and find yourself back to back in bed with an unconscious violinist. A famous unconscious violinist. He has been found to have a fatal kidney ailment, and the Society of Music Lovers has canvassed all the available medical records and found that you alone have the right blood type to help.

They have therefore kidnapped you, and last night the violinist’s circulatory system was plugged into yours, so that your kidneys can be used to extract poisons from his blood as well as your own. The director of the hospital now tells you, “Look, we’re sorry the Society of Music Lovers did this to you — we would never have permitted it if we had known. But still, they did it, and the violinist is now plugged into you. To unplug you would be to kill him. But never mind, it’s only for nine months. By then he will have recovered from his ailment, and can safely be unplugged from you.”

Is it morally incumbent on you to accede to this situation? No doubt it would be very nice of you if you did, a great kindness. But do you have to accede to it? What if it were not nine months, but nine years? Or longer still? What if the director of the hospital says. “Tough luck. I agree. but now you’ve got to stay in bed, with the violinist plugged into you, for the rest of your life. Because remember this. All persons have a right to life, and violinists are persons. Granted you have a right to decide what happens in and to your body, but a person’s right to life outweighs your right to decide what happens in and to your body. So you cannot ever be unplugged from him.”

Instead of arguing that the foetus does not meet the criteria for personhood, Thomson turns the argument on its head. Even if one were to accept the premise of the traditional supporter of those who uphold the moral status of the foetus as a person, Thomson argues that the woman is morally justified in having an abortion if she wants to. A person, Thomson argues, is not morally obliged to sustain the life of another — even if the other being poses no threat to her life.

It might be easier to view the person who stays connected to the violinist despite not wanting to as committing a supererogatory act. She goes above and beyond what is required, and thus surely she displays some virtue of compassion, or benevolence. However, for Thomson, this does not entail that she is obligated to perform such an act.

By the same token, if the kidnapped woman chooses to disconnect herself from the violinist, she does not commit an immoral act. Although both the violinist and the foetus may have a right to life, this is not extended to a right to use another being in order to facilitate that right to life. The woman is justified in removing the foetus, and thus ending its use of her body which she does not desire.

It’s worth noting that there have been numerous objections to Thomson’s argument, from both sides. Her argument is that a person has autonomy over their own body, and therefore another being cannot use it to prolong their own life. What about when the technology is sufficiently advanced so that a foetus can be brought to term safely outside the womb?

Another objection deals with terminology; in the case of the violinist, he has no right to sustain his life through being connected to her kidneys. In the case of the foetus, it has no right to sustain its life through being connected to the mother if she does not wish it. Some have said that this is an argument that a woman has the right to remove an unwanted entity from her body; and this can be divorced from the argument that a woman has the right to end the existence of a foetus.

It’s also worth noting that Thomson’s argument is directed at those who deny a woman or girl an abortion based on rape or maybe in situations like incest. She is trying to make the argument that anyone who hasn’t freely chosen to have sex — leading to the possibility of pregnancy — shouldn’t have to remain pregnant if they do not want to, and pregnancy occurs. She does make further arguments — using thought experiments — against a whole host of possible circumstances that pregnancy could occur in, including the case of failed contraception. The violinist argument is the most quoted, however.


Physicalism is, simply put, the idea that there is nothing but the material world. It’s widely considered to be very plausible. But some are unsure as to how the phenomenal — the conscious experience — can either supervene on the physical or be a part of the purely physical. Some philosophers asked questions like, “how can our thoughts have content?” and “what is the nature of perception and perceptual states?”

This is a really important part of our experience; our experience of what it’s like to be human. Nagel says that, “fundamentally an organism has conscious mental states if and only if there is something that it is to be that organism…we may call this the subjective character of experience”.

Physicalism has long since troubled philosophers of metaphysics. It’s simpler, and therefore easier, to characterize everything as physical. Allowing for something else — the phenomenal — as being something of an entirely different calibre opens up a whole realm of problems. How do the mental and the physical interact, for instance?

Type-Identity Physicalism is one kind of physicalist position that denies that mental states exist “over and above” physical states — that they supervene on them. It’s important to note that this position doesn’t claim that the mental doesn’t exist, or that brain states are everything. Rather, it states that the mental does exist, but our “folk-psychological” ascriptions are the same thing as these brain states — they can be identified with them.

Take pain. We all know what it’s like to be in pain. Pain hurts. A key characteristic of pain is that it hurts. It’s a mental phenomena. Sure, you might fall over, and feel pain. Falling over might mean that you graze your knee, and then you feel a really sharp surge of pain. So pain might come alongside damage to a body, but it doesn’t always result in damage. Heartbreak is a kind of pain, and melancholy, and that’s all mental. Pain is a mental phenomena that follows — sometimes — damage to an organism.

For the Type-Identity Physicalist, pain is identified with a certain neural phenomena. Pain is C-fibre stimulation. A type of mental event describes one type of physical event. Whenever a creature undergoes C-fibre stimulation, it experiences pain. What this means is that a creature without C-fibre stimulations cannot experience pain.

Some thinkers have been critical about this. Say fish or bees don’t have C-fibres in their nervous systems, then they don’t feel pain. But they certainly seem to exhibit behaviour that suggests they experience pain; Michael Tye has a recent book where he speaks of the titular “shell-shocked crabs”. The crabs exhibit certain behaviour associated with pain; they move away from the source of pain, for example. Peter Singer’s label “speciesism” may be applicable to those who refuse to ascribe the capacity to feel pain to those animals who simply are not built like human beings. It’s kind of like the xenophobe who condemns a foreigner for speaking a different language to herself.

It also denies the possibility of there being other life in the known universe that don’t have C-fibres, but do experience pain. It’s at least conceivable; there may indeed be intelligent life forms that are built in an entirely different way to us, but do indeed experience pain. The idea that creatures with different sorts of brains could all experience pain means that pain, as a mental state, is multiply-realisable. It can be brought about in a whole host of possible ways. Maybe some animals could have Y-fibres, or Z-fibres, and they feel pain.

Interestingly, Michael Tye advocates for an approach where we judge whether something can feel pain based on its behaviour first — and its biology second. This will stop our preconceived notions of neuro-physiology, as based on our own experience, from clouding our vision.

Many early evolutionists taught that women were inferior to men because they had smaller brains. One argument against women’s political emancipation was that they had smaller brains and so would vote unwisely. “Women simply had inferior brains, which made them unsuited to the rigors of voting,” says Cheryl Jorgensen-Earp, a professor at the University of Lynchburg. A recent study has claimed that women have more efficient — albeit smaller — brains than men.

You can see why people with big brains (biological men) might have believed that a big brain meant somebody was more intelligent. But it was a case of one’s own experience clouding judgement.

Frank Jackson came up with a novel way of denying the possibility of physicalism. It’s worth noting that Jackson changed his mind a few years later, and reverted back to arguing for physicalism. But the thought experiment is still used today. James Robert Brown and Yiftach Fehige describe Jackson’s idea like this:

He formulates the argument in terms of Mary, the super-scientist. Her story takes place in the future, when all physical facts have been discovered. These include “everything in completed physics, chemistry, and neurophysiology, and all there is to know about the causal and relational facts consequent upon all this, including of course functional roles” (Jackson 1982, p. 51). She learns all this by watching lectures on a monochromatic television monitor. But she spends her life in a black-and-white room and has no color experiences. Then she leaves the room and sees colors for the first time. Based on this case, Jackson argues roughly as follows. If physicalism were true, then Mary would know everything about human color vision before leaving the room. But intuitively, it would seem that she learns something new when she leaves. She learns what it’s like to see colors, that is, she learns about qualia, the properties that characterize what it’s like. Her new phenomenal knowledge includes knowledge of truths. Therefore, physicalism is false.

Jackson was attempting to introduce the notion of qualia; that there’s a certain kind of quality to experiences, and this is part of what makes us human. There’s something that it’s like to see a colour, and that isn’t contained in facts about the colour, or by what goes on in the brain when we experience colour.

For the physicalist, all facts about mental states are physical in nature. The phenomenal does not supervene on the physical. But the Knowledge Argument, as the thought experiment came to be called, suggests that there’s something more to our experience than what can be considered explained by the physical or even the factual.

But that thought experiment was rivalled by Daniel Dennett:

Instead of a red tomato, Dennett, in his version of the thought experiment, presents Mary with a bright blue banana. In his version of the story (which seems just as plausible as Jackson’s), Mary balks and says she is being tricked, since she knows that bananas are yellow, and this, says Mary, is a consequence of knowing everything physical about colour perception. Mary does not learn anything new when she sees coloured objects for the first time, so there is no case against physicalism after all. Jackson’s initial thought experiment was very persuasive, but Dennett’s was equally so, thus, undermining Jackson’s argument.

There were other responses to the problem, besides Dennett’s: one objection was that Mary doesn’t learn new facts — she instead learns a new kind of ability. David Lewis, in his 1988 work ‘What Experience Teaches’, claims that ‘The Ability Hypothesis says that knowing what an experience is like just is the possession of these abilities to remember, imagine and recognize…it isn’t knowing-that. It’s knowing-how.’ Is this correct?

Another objection centered around the distinction between knowledge and facts, claiming that what Mary gains is new knowledge, but that it concerns old facts — these facts being presented differently in first-person experience than third-person learning. Is this a bit of a cop-out? It’s hard to say.

Whatever you think, the Mary Thought Experiment has been critical in shaping Western Philosophy of Mind. It’s also influenced so many other aspects of philosophy; from Aesthetics to Epistemology. I’m hoping to start my PhD next year, and I’ll be working on how the Knowledge Argument can help us understand how we learn from reading fiction. Ironically, it’s not a novel idea; I’ll be following László Kajtár’s work on the topic. But I think it can explain how we might learn from fiction — even when we’re unsure what we’ve learnt in a factual sense.

A Philosopher’s Stone

A place for a discussion of the ideas all around us in…

Lizzie Bestow

Written by

BA & MA in Philosophy from Durham University, off to do a PhD in September! I write accessible Philosophy pieces for those who’ve never studied it.

A Philosopher’s Stone

A place for a discussion of the ideas all around us in society, culture, philosophy, and more.

Lizzie Bestow

Written by

BA & MA in Philosophy from Durham University, off to do a PhD in September! I write accessible Philosophy pieces for those who’ve never studied it.

A Philosopher’s Stone

A place for a discussion of the ideas all around us in society, culture, philosophy, and more.

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