It is generally agreed that perception involves a real object transferring information about itself into the brain of the perceiver, via the sense organs and nerves; and the distinguishing features of this are that the real object is external to the perceiver and public, while the image of it in the brain is internal and private. My question is: illusions are unreal, but they are external and public --- as with the railroad lines meeting in the distance, or the Sun and the Moon being the same size during an eclipse. So are illusions real, or unreal?
Illusions are "real" in one sense and not in another. Unreal: The railroad lines look to me as if they meet in the distance, but they don't. In this case, reality isn't as it appears to me. Real: I am part of reality, and so are my mental states. One of those is that the railroad tracks (falsely) appear to me to meet in the distance. This is a robust illusion that I and many others are really subject to.