You've probably heard of the infamous Trolley Problem (we devoted a whole episode to it back in 2013), but you may not know that it owes its name to Judith Jarvis Thomson. Philippa Foot, one of the other philosophers that we’re featuring in this Wise Women series, came up with the original thought experiment; but Thomson developed it, and it's her version that ended up becoming something of a pop-culture phenomenon.

Thomson asks us to imagine a runaway train (or "trolley") that’s about to run into five people working on the track. If you do nothing, the train's going to kill them all. Fortunately, you happen to be standing next to a lever, and if you pull it the train will go onto a different track, killing just one unfortunate railway worker. What do you do?

Presumably, most of us would pull the lever—after all, why let five people die when it could be only one? Still, that doesn't mean that there isn't something troubling: that poor worker's blood is now on your hands. Isn't there a difference between actively killing people and letting them die?

You might think that distinction doesn't matter; the only thing that counts, here, is saving the maximum number of lives. And that sounds very reasonable until you consider another of Thomson's scenarios. Imagine if a doctor has five patients in need of transplants: one needs a liver, two need a lung, two need a kidney. By murdering just one healthy patient, the doctor can save all five lives. Should she do it? Seems like the answer has to be no. It’s not just the outcome that matters: even if you can save five people, there are some things you just can’t do to bring that about.

So is Thomson saying that even if the consequences are good, it's never ok to cause harm to another person? Not quite! Here's where yet another fascinating thought experiment comes in.

Here, you wake up in a hospital room and discover a whole bunch of tubes and wires coming out of your body. Where do those tubes go to? Answer: a violinist! It's the greatest violinist of your age, and that violinist is very ill. The doctors have hooked the two of you up so that you can keep the violinist alive. The treatment will last, oh, about 9 months, at which point you'll be free to go. But for now you are the violinist's life support system. 

Do you need to stay in the hospital, hooked up to all these tubes? Or are you ethically entitled to leave? You never agreed to this. And as Thomson argues, no one is entitled to use your body without your consent—not even the greatest violinist in the world. Here, it seems, you are permitted to cause a degree of harm to another person, just as you were in the trolley case.

Believe it or not, the violinist thought experiment is designed to teach us something about the ethics of abortion. We'll find out more about that, about Thomson's moral theory, and about her delightfully outlandish thought experiments from our guest, who actually studied with Thomson. It’s Elizabeth Harman from Princeton University, author of “Creation Ethics: The Moral Status of Early Fetuses and the Ethics of Abortion.”