Reality is like a black box with an input entrance and an output exit. You know what goes in and what goes out. You can test this box every way you want; if you do enough tests, you can even predict the output, given the input. This way, controlling the inputs, you can control the outputs. In short, you can have knowledge of box's inputs/outputs, can predict and control them. But you'll never know, not even hope that you'll ever have a truly knowledge of what's inside the black box, what this box REALLY is. The black box is a trivial metaphor of Kant's "the thing in itself&".
From this example one can conclude that the thing observed is defined in fact by an interaction between the observer (subject) and the observed (object). The object (black box) has no sense without the IN/OUT wires, it is nonexistent.
There are two texts I want to discuss, both being in my personal favorites top.
First is Plato's cave allegory. It is one of the most famous philosophical texts, so I'll not insist on it. As a personal remark, it resemble Matrix's kind of approach on reality/appearance topic.
The second text is the story "Reason";, from the Isaac Asimov's "I, robot";. For those who doesn't read it, it's about two astronauts, Donovan and Powell, and an android, QT-1 nicknamed Cutie. The problem was that Cutie, who was built by the two in order to replace man in space working, was from the start a hardcore rationalist, a robotic Descartes. His personal philosophy was to believe only in his own rationality, on the premise that having a much more superior intelligence, physical force compared to humans, they couldn't built him since an inferior being is not capable to construct a superior one. So Cutie started to create his own mythology, with a personal Master, a genesis, etc. No matter how hard the two men tried to convince Cutie about the real world, giving him all kinds of evidences, the robot could found counterarguments all the time. The crisis sprang when Cutie took over the whole station, not allowing the men to get near the controls, all this in a critical moment when was required someone skilled to run the station's controls in order to save the Earth from a disaster. Surprisingly, the robot managed the situation very well, but under totally different reasons.
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"Mike, Mike!" He was shaking the other madly. "He held It steady!"
Donovan came to life. "What? Wh-where-" And he, too, gazed with bulging eyes upon the record before him.
Cutie broke in. "What is wrong?"
"You kept it in focus," stuttered Powell. "Did you know that?"
"Focus? What's that?"
"You kept the beam directed sharply at the receiving station - to within a ten-thousandth of a milli-second of arc."
"What receiving station?"
"On Earth. The receiving station on Earth," babbled Powell. "You kept it in focus."
Cutie turned on his heel in annoyance. "It is impossible to perform any act of kindness toward you two. Always the same phantasm! I merely kept all dials at equilibrium in accordance with the will of the Master."
The first example states that beyond "the shadows", the appearances of this world there is a transcendental, unchangeable, ABSOLUTE reality but eventually someone could get knowledge about it (Neo swallowing the red pill). It is the hope that eventually we'll find out what the black box containes. The problem with this hypothesis is that nothing, nobody could guarantee that this newly discovered world is actually the REAL one. Perhaps it is just another dream, in a dream, in a dream ...(or nightmare).
In Asimov's story Cutie created a logical consistent world, keeping all station's parameters right, even if he has totally different interpretations about his own actions. That was another version of reality, seen trough a robot's eyes. Reality is RELATIVE this time. Since reality has a meaning only if is related to an observer, it is obvious, due to the number and quality of observers, that there are multiple realities. I don't say that in the absence of observers there's no reality. I just think that is a nonsense to talk about reality/appearance in the absence of any observers.