[Note. There will be two postings per week until December.]

A decade or more ago, I was reading Thinks, a book written by David Lodge. As with other Lodge novels, it was set in an academic institution. One day as I was coming home from work on the subway I got to the part of the book where the chief character, a cognitive scientist, is showing a novelist the science building, which has a mural inside with scenes that relate to consciousness. One portion of the painting depicted bats. The novelist is puzzled by this, and the scientist explains that the philosopher Thomas Nagel had posited that no one could know what it was like to be a bat, a thought experiment to show how difficult it is to understand consciousness.

I had gone home only to change my clothes, and within a short time I was driving across town to play tennis. In those days, I regularly listened to audio books in addition to reading “real” books, and in the car that evening I was listening to John Banville’s The Sea. Banville’s narrator said that he liked birds as a boy, but not to identify them. Instead, he found their nests and imagined what it was like to be a bird. Then, although not using Nagel’s name, he referred to the same bat story that was in Lodge’s book, with the narrator’s point being that if anyone could have understood what a bat was like, he could have as a boy.

I was struck at the unlikelihood of perceiving two references to this same thought experiment in an hour when I had never heard of it before. A couple days later, I said something about this to a friend, who knew many things I did not. Harry was not surprised in the least by the references to bat consciousness. He was well aware of Nagel’s assertion, and in the nicest way possible indicated that Nagel’s thought experiment was quite famous. And once again I learned some of the deficiencies in my education.

This came back to me when over drinks recently I started to tell a different friend about a different thought experiment I had just read about. Before I finished relating it, I could tell that she was already familiar with the hypothetical. Again, I realized that I was not well versed in thought experiments, even when they were famous to others. But maybe you are like me in that regard, which gives me the chance to outline this particular thought experiment.

Assume you are operating a runaway train that went out of control through no fault of yours. If you do nothing, the train will kill five people who are on the track ahead of the train. If you divert the train to a siding, which you can do, the train will not kill the five but will kill only the one person who is on the siding. In one case you are passive and five die. In the other, you take an action that kills someone. What is the just and fair (or defensible) course of conduct?

Apparently, most people who are asked about this thought experiment say to divert the train. But now change the hypothetical. Instead of operating the train, assume that you are on an overpass witnessing the runaway train and you see the five people that will be killed if the train does not change course. Next to you on the overpass is a very large man leaning over the parapet, and you see that if you push him off the overpass he will fall on the tracks and be killed, but his body will divert the train and save the five. Would it be just and fair if you took this action?

Perhaps you have already pondered this thought experiment, thought it completely through, and come to your conclusions. I am still working on it.