Philosophy
The Epistemology of Perception and the Argument from Illusion
Quick fact
The argument from illusion, famously deployed by philosophers like Descartes and A.J. Ayer, uses the possibility of perceptual error—such as seeing a round coin as elliptical—to argue that we never directly perceive physical objects, only mental representations called 'sense-data'.
Why this is interesting
When you look at a white wall, you see it as white. But if the lighting changes, you might see it as grey. Does that mean you ever really see the wall at all?