Even though I think violinists and fetuses are sufficiently different from each other that Judith Jarvis Thomson’s thought experiment doesn’t have a lot of bearing on the abortion debate, I want to back up and address it on its own terms ... or actually on slightly revised terms. Here is her statement of it:
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. ... 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.
It’s been a while since I’ve read Thomson’s article and I’d forgotten about the kidnapping element. I don’t see an analog to kidnapping in most situations involving abortion, so I’ll take the liberty of modifying that element. You wake up and find a famous violinist attached to you by magic. The universe does this from time to time randomly. Neither you nor the violinist nor the Society of Music Lovers is at fault. It’s just one of those things.
Also, for the sake of this thought experiment, let’s make the violinist conscious so that he can state his preferences and engage in some negotiation. (Alternatively, he could have expressed his preferred way to handle this situation before he was rendered unconscious.)
Suppose the violinist wishes to remain plugged into you instead of dying, while you wish to unplug him. What rule should we adopt? Which of you should get to decide what happens?
The Coase Theorem tells us that, in the absence of transaction costs or other factors that would distort free bargaining, the rule we adopt doesn’t matter. (More precisely, it matters only to distributive concerns, not to the behavioral result.)
If the violinist values remaining plugged in at $3 million while you value unplugging him at $150,000, he’s going to remain plugged in no matter which of you gets to decide his fate. If he gets to decide, there’s no amount of money you’d be willing to pay him that would cause him to agree to be unplugged. If you get to decide, you’ll arrive at a bargain to let him stay plugged in for somewhere between $150,000 and $3 million. Either way, he’s going to stay plugged in.
In the real world, there are transaction costs and other factors to consider, such as the extremely unequal bargaining position between the two of you. He’s completely desperate at this point, so it’s less of a free negotiation than a stick-up.
One of the corollaries of the Coase Theorem is that, in the face of transaction costs or other barriers to free negotiation, we should pick the rule that defaults to the result that would have been arrived at in the absence of those barriers.
I suspect that, for the most part, violinists would value remaining plugged in more than non-violinists would value unplugging them, so the default rule should be that the violinist should have the right to remain plugged in unless you agree to pay him enough so that he agrees to be unplugged.
(There’s nothing special about violinists as a profession, obviously. Designating the person’s job just makes the thought experiment more vivid. But in this hypothetical universe, all people are equally likely to be “violinists” regardless of their profession.)
Insurance could help with this. Since being on either end of the plug is randomized, there’s no moral hazard problem with insurance. However much money would make you indifferent between letting the violinist remain plugged in or getting to unplug him, you could buy insurance for that amount. Or maybe we could fund universal coverage through taxes.
In any case, I suspect that if we all have to take turns rolling the dice, with an equal likelihood of ending up on either side of the plug, we’d collectively agree that a default position of remaining plugged in is better than a default position of unplugging.