Blue.

Is my blue your blue?

You and someone else look at the same things and use the same colour words. But do your colours look the same inside?

What they see

Nobody can see through someone else’s eyes.

Tap anything to ask them what colour it is.

The breadcrumbA little history of who else got stuck here.

In 1690, John Locke wondered whether two people might experience colours differently inside while still using all the same colour words.

A violet could give you the experience that a marigold gives me, and neither of us would ever know. We would still call the violet blue, call the marigold yellow, and agree about everything we pointed to.

For Locke, that wasn’t necessarily a problem. The words still worked.

Later philosophers pushed the thought further: if the difference could never show itself, how could we ever know what another person’s experience is like from the inside?