There’s a famous thought experiment by Frank Jackson about a woman named Mary who, while having normal vision, is raised in a black-and-white environment. While in this environment, Mary learns everything there is to know about color – the physics of light waves, reflectivity, the physiology of the cones and rods in the eye, etc. Jackson argues that when Mary leaves the black-and-white room, and sees something red for the first time, she’ll learn something new. And since she already had all the physical knowledge there was to have about color, this new thing she learns is non-physical. Which shows that there are facts beyond the physical facts, and thus that physicalism is wrong.

Here’s a link to the .pdf of the article where this first appears – called “Epiphenomal Qualia”.

In that same article, Jackson first discusses a similar thought experiment, about a man named Fred who can see an additional shade of red that no one else can see. He proves to the satisfaction of scientists, via observation and experiment, that he’s really seeing this other shade.

Jackson’s point here is similar: we can learn everything physical there is to know about Fred (using brain scans, doing an autopsy after his death, etc.), but we still won’t know what that extra shade of red looks like. So despite having all the relevant physical knowledge, we’ll still lack the knowledge of “what it’s like”. So this knowledge must not be physical knowledge, and hence physicalism is false.

What got me thinking about all this is an article someone linked to on Twitter recently about a woman who sees many more colors than the rest of us. She’s Fred times 100! It made me wonder if Jackson knew about this condition when he wrote the article, or if he’s learned about it since.

It also gets me thinking about the more general question: do many thought experiments in philosophy (or anywhere else) actually come true? And when it does happen, does it matter? Does it add support, or undermine the point of the original thought experiment? Or are different cases going to be different?

Another related issue is whether or not thought experiments can be proven false, or impossible. Clyde Hardin was a professor at Syracuse University when I was a graduate student there. Hardin is famous for writing a book called Color for Philosophers in which he allegedly splashed some empirical cold water on some thought experiments related to color – specifically, the famous Inverted Spectrum thought experiment. In this thought experiment (sometimes used as a paradigm example of a philosophical 2 a.m. dorm room topic of discussion), two people have exactly opposite color vision – i.e. when one sees red the other sees violet. Where one sees ROYGBIV the other sees VIBGYOR. The thought experiment is drawing attention to the private nature of our qualitative experiences (much like Jackson’s do) and the impossibility of knowing whether others are really experiencing the world in the same way that we are.

Hardin apparently (I’m using such qualifiers because my memory’s a bit hazy since I haven’t read the Hardin book in years) showed that such inverted spectra are impossible. The thought experiment, though, still gets a lot of play, and I’m not sure Hardin’s takedown had any effect. Perhaps it shouldn’t, since it’s generally not the case that thought experiments have to be physically possible to serve their purpose (e.g. Einstein’s thought experiment about riding on a photon).

Anyway, thought experiments are definitely one of the most interesting aspects of many philosophical discussions. So it’s a topic I’ll no doubt return to.