The philosopher Thomas Nagel posed the curious question, What is it like to be a bat? To the extent that an organism has conscious mental states, he argued, “there is something it is like to be that organism.” Every conscious organism must have private, directly apprehended mental states that define “what it is like” to be that organism. Known as “qualia,” these subjective characteristics of experience include qualities like the pain of a stubbed toe or the redness of a red, red rose.
Nagel wanted to know what it is like to be a bat because bats are so different from us. They perceive the world primarily through echolocation, bouncing sound waves off objects in the environment to determine their size, shape, and motion. This is nothing like how we perceive the world, so there is little in our direct experience to suggest what it must be like to be a bat. A bat’s qualia are inaccessible to us.
Nagel concluded from this thought experiment that we can never know what it is like to be a bat and, therefore, that there are facts we can neither comprehend nor express in language. “I want to know what it is like for a bat to be a bat,” he wrote. “Yet if I try to imagine this, I am restricted to the resources of my own mind, and those resources are inadequate to the task.