What is reality?
Answer by Helier Robinson
There are three usual definitions of reality.
The first is that reality is all that we perceive around us that is potentially universally public. These three conditions apply for the reason that some of what we perceive around us is illusory. You might be wearing coloured sun-glasses, for example, so that the moon appears to be blue. But you quickly discover that this blue moon is private to you. Such private perceptions are illusions, and unreal. They are mis-representations of reality. Another example is that everything visible appears smaller with distance. Imagine a straight road with telephone poles along it: with distance, the road gets narrower, the poles get shorter, and the poles get closer together; visible space shrinks with distance in all three dimensions. Artists have to use a special kind of geometry, projective geometry, to draw visible space correctly. But this shrinkage, although public, is illusory. Suppose that you are on a straight road on the way to meet your friend and you see her in the distance; you text her that you can see her in the distance and that the road appears to be very narrow where she is; and she will reply that it is wide where she is but narrow where are you are. So this illusion, although public, is not universally public. But we cannot achieve universal publicity, so we say that the real is what we perceive around us that is potentially universally public. This kind of reality might be called empirical reality, since the empirical is all that we know through perception.
The second definition of reality is that it is all that exists independently of human perception, or even of human consciousness. That is, it exists regardless of whether anyone perceives it or not. Included in this reality are things which cannot be perceived but for which we have good evidence: electrons, black holes, minds other that one’s own, empirical objects when no one is perceiving them, etc. This kind of reality might be called theoretical reality, since the theoretical is non-empirical.
The third definition of reality is that it is all that makes true propositions and beliefs, true. It is the ground of truth, in other words.