Full Idea
If I stare at a white wall with my brain wired to a virtual reality computer, and it generates a white wall, we wouldn't say I am seeing reality. It seems that the wall itself must in some way cause my perception of it.
Gist of Idea
Appearances don't guarantee reality, unless the appearance is actually caused by the reality
Source
Jonathan Dancy (Intro to Contemporary Epistemology [1985], 11.4)
Book Reference
Dancy,Jonathan: 'Introduction to Contemporary Epistemology' [Blackwell 1985], p.173
A Reaction
But suppose the computer generated in my mind an image of the wall which was actually in front of me? And suppose the computer got its image from the identical wall next door, not from mine? And it was only judged identical because the architect said so