The philosophy of mind has a long history of "thought experiments": experiments that aren't actually possible, but that philosophers like to imagine in order to clarify their intuitions and ideas. John Locke asked about the "inverted spectrum". If Alice sees colours the opposite way round to Bob, so that she experiences red where he sees blue, and vice versa, how could we ever know? And if we can't, doesn't that prove it's impossible to know how anyone else perceives the world? Douglas Hofstadter had the fable of Mr. Chase and Mr. Sanborne that I told in the previous post. And in 1974, philosopher Thomas Nagel wrote a famous paper titled "What is it Like to be a Bat?"
Bats, Nagel says, are alien. They perceive their world by sonar, computing the distance, size, shape, movement, and texture of objects from the way these reflect their own high-frequency shrieks. This is such a different sense from any we possess, so is there any way to know what the bat experiences? He concludes that we can't. Even if you try imagining that you have webbing on your arms, fly around at dawn and dusk catching insects in your mouth, locate these by sonar, and spend the day hanging upside down by your feet in an attic, that only tells you what it's like for you to be a bat. The bat's brain is wired so differently from ours that it says nothing about what it's like for the bat to be a bat.
Nagel isn't especially interested in chiroptology or in emulating Doctor Dolittle: his bat is a stand-in for "any sufficiently different mind". For me, the class of "sufficiently different mind" is the girls I see with holes gaping in the knees of their jeans. What aesthetic pleasure do those give them? When I look at clothes, my attention immediately seeks beauty: vivid colours, graceful flowing lines, intricate embroidery, patterns you can get lost in. I know what it is like to want and enjoy these. And the girls with holes in their jeans must get joy from those, else why wear them?
But even if I try imagining myself feeling intense pleasure while gusts of winter air blast around my red knobbly knees and passers-by stare at me as if I've crawled out of the poorhouse, that only tells me what it's like for me to be one of those girls. It says nothing about what it's like for those girls to be those girls.