Think
I'm reading "Think," by Simon Blackburn. It's not the liveliest philosophical writing, certainly not compared to the witty "...in 90 Minutes" series by Paul Strathern. (I recommend the latter for the sheer entertainment value of the author's style, if not the substance.)

"Think," isn't bad though, and I like using Descartes as a launching point, since he's relatively easy for a modern reader to grasp, and his thought touches on most of the broad philosophical areas.

On the section on Philosophy of Mind, however, the author makes a couple of basic errors. The author discusses the problem of perception and private languages. Meaning, when I see a picture, I see colors such as blue and red, but how do I know that when you see the same picture you see the same colors? For example, when you see the wavelength that I call "blue," the color you actually perceive in your mind is "red." You still call it "blue," because we share the "public language" of color, but if I could somehow get inside your mind, I'd call it "red."

A simple way to explore this idea is to pretend that we can only see in black and white. Could some people see black as white and vice versa? Imagine that such people, when they look up in the night sky, see the moon and stars as dark spots, and the emptiness in between as whiteness. Let's call these people "Negatives."

Negatives can get along perfectly fine in the world. Yes, when they see the moon, which to them looks black, they still call it "white," just as us Positives do, because they've learned the public language of black & white.

Now, could Negatives actually exist? Is a reversed monochromaticism even possible? Blackburn suggests it's not:

But this does not really work. If I make a piece of grey glass lighter, I see better through it; if I make it darker, I see less well through it. Since he is a physical duplicate, this has to be true of my twin. But for him, when we clear the glass it 'seems' as though we added soot, since it becomes subjectively darker. And when we add soot it 'seems' as though it is becoming clearer. But then we have to imagine that for him, as a plate of glass becomes darker he sees through it better and better, and as it becomes lighter he sees through it worse and worse. And that just doesn't seem to make sense. It doesn't mark a coherent possibility.

But I think the author has made a mistake here, in confusing lightness with transparency. Just because something becomes "lighter", doesn't mean it becomes clearer. Take a piece of glass that's been painted white, for instance. You can't see through it, but it's certainly not "dark." And thus, if you had a piece of glass and you added soot to it, it'd appear darker to a positive and lighter to a negative, but in both cases, it'd become less transparent. Neither the Negatives nor the Positives could see through it, even though subjectively it appears at opposite ends of the light/dark spectrum.
- posted by mike @ 6:08 PM