Thomas Nagel

It was the philosopher Thomas Nagel, I think, who came up with the thought experiment of trying to imagine what it's like to be a bat - though I suppose any animal would do. The point is, of course, that you can't, just as you can't know what it's really like to be another person - I mean know rather than imagine. How much can we know of what goes on in another person's mind? We observe people, watch what they do, listen to what they say - and other sounds they may make - see how they respond to their environment, their likes and dislikes, what they eat, and so on. And from this we have learned to make fairly accurate predictions about how they'll behave in certain situations, yet we still can't be sure what thoughts have passed through their minds and certainly not what it feels like to them. We can guess, based on personal experience in similar situations, so we must assume that humans are alike enough for us to be reasonably certain that, for example, we experience the color red in roughly the same way, or in the same ways. But, again, to you red might bring to mind thoughts of blood and death, whereas to someone else warmth or excitement. And the differences can't just be cultural.