Why our experience and the object we experience are one

Step 11: The argument from illusion

Sometimes, we see something as though it were different from what we know it ought to be. We see two lines as though they were curved while we know they are straight. Or we see a colored patch where we know there is only a black and white pattern. Are these cases in which experience departs from reality? Contrary to common sense, they are not.

Example. Consider a mirage. Tom looks at the heated sand and sees a watery surface. Does the sand look like water? No, it does not. The heated sand looks just like heated sand should look. Both water and sand share the same property but, since one more often sees water than heated sand, most people attribute a mirror-like behavior to water, rather than to sand.

Illusions are a perception of real physical properties in the world and not cases of illusory mental properties. For instance, one cannot directly perceive whether a substance is made of water or sand. Thus, one's visual system must go after a proxy physical property that often co-occurs with water — in this case, a mirror-like behavior. In short,

Illusions are a mismatch between what one believes one ought to perceive and what one actually perceives.

Riccardo Manzotti, 27 January 2015 (updated December 25st)