What Is Real · ages 9–12
Is red in the apple or in you?
Your red might be what I call green. Neither of us would ever find out. Does that matter?
Look at a ripe apple. It is red. Now ask what part of that redness belongs to the apple.
Physicists describe light of a particular wavelength striking a surface, and eyes detecting it, and nerve signals, and — eventually — an experience. Every step in that list can be measured except the last one. The redness is not in the light, which is only a frequency. It is not in the apple, which reflects light without being coloured in any measurable way. It appears at the end of the process, in the seeing.
Galileo took this to mean that colours live in the perceiver, and that the real world contains only size, shape and motion. Locke tidied it into a distinction: primary qualities are genuinely in the objects, secondary qualities are effects that appear in us. Berkeley then pointed out the trouble. The arguments that push colour into the mind push shape and motion there too — every quality is known only through experience. If colour is a deception, the same reasoning rules out the apple entirely.
There is one more twist, and it is the one children find best. It is possible that your red is exactly like what I would call green — and neither of us could ever detect it, because all we can compare is what we say, not what we see. Nothing in science can rule it out. That is not a puzzle with an answer; it is a permanent limit on what any of us can know about anyone else.
Try it
Look at one patch of colour, then at another, then back at the first. Notice whether the first changed. Now decide which of the two you saw was the true one.
What do you think?
Do you think there is a right answer to this question?
Talk about it
- Are colours properties of things or of perceivers?
- If nobody could see, would red still exist?
- Why do we agree about colours at all?
Yes, but… — the arguments people actually make
Colour is a wavelength. That is a fact.
A wavelength is a measurement of light. The redness is what happens when that light meets an eye and a brain, and machines can measure the first without any colour appearing.
If red weren't in the apple, everyone would see different colours.
Everyone's eyes are built the same way, so the same input produces the same experience. Agreement is evidence of shared machinery, not of shared facts out there.
Who cares? I still see red.
You also see vivid colour in dreams, and in pictures that are only grey. Which means your experience of colour is produced by you, whatever the apple is contributing.
What other philosophers think
- GalileoArgued that tastes, smells and colours live in the body that perceives them, not in the object — the physical world has only size, shape, motion.
- John LockeFormalised this as primary and secondary qualities: shape is in the thing, colour is the effect it produces in you.
- George BerkeleyPointed out that this argument proves too much, since the same reasoning applies to shape and motion. If colour is in the mind, so is everything else.
If you want to go further
- An Essay Concerning Human Understanding — John LockeThe primary/secondary quality distinction, in Book II.
- Three Dialogues between Hylas and Philonous — George Berkeley1713. Berkeley takes Locke's argument and pushes it until it breaks.
Most of these were written for adults, which is why it is worth reading them with someone older.