What is consciousness? (Philosophy HL)

The big idea: Bite into a lemon. There's a sharp, sour taste — and there's something it is like for you to have it.

That 'what it's like' feel, right now, is consciousness. It sounds like the most obvious thing in the world, until someone asks you to explain it — and you can't.

Philosophers give the feel a name: qualia. The sourness of the lemon, the ache of a bruise, the exact blue of the sky you see — each has a feel that is yours.

Hold onto this: Consciousness isn't being clever or awake in general — it's that there's something it is like to be you from the inside. A rock has no inside feel. You do.

The sharpest way to feel the puzzle comes from the philosopher Thomas Nagel.

Nagel: the bat: A bat finds its way in the dark using echolocation — it squeaks and 'sees' the world by the echoes bouncing back. Nagel asks: what is it like to be that bat, sensing the world by sound?

You could learn every fact about a bat's brain and its squeaks. But you still wouldn't know what it feels like from the inside to be one. There's an inside view that all the outside facts miss.

Checkpoint — Nagel: In one line: there's something it is like to be conscious, and knowing all the brain facts doesn't tell you what that is. The next thinker turns this into a sharper trap.

The philosopher Frank Jackson built a story that makes the gap impossible to ignore.

Mary's room: Mary is a brilliant scientist who has lived her whole life in a black-and-white room. She has learned every physical fact about colour — the wavelengths, the eye, exactly what the brain does when someone sees red.

One day she walks outside and sees a red rose for the first time. Does she learn something new?

Most people say yes — she finally learns what red actually looks like. But she already knew all the physical facts. So the feel of red must be a fact the physics left out.

Go further — higher-level insight: Nagel's bat and Jackson's Mary are two versions of one move — the knowledge argument: complete physical knowledge still leaves out the feel. The sharpest reply is that Mary gains a new ability (knowing-how), not a new fact (knowing-that). Naming that reply is a top-band move.