Who knows if the books, when nobody and nothing is watching, will change their form or just disappear?
As we can't experience non-experience, we can never know whether or not the things we perceive do also exist in an absolute sense.
For all we know, nothing exists beyond our minds, which Berkeley believed.
According to him, the reality of the outside world depends on the "knower." He proposed his position using three Latin words: Esse est percipi, meaning "To be is to be perceived." Even though he wasn't a solipsist, Descartes made an observation fundamental to solipsist philosophy.
He concluded that the only truth he couldn't rationally doubt was his own existence. Hence, his famous words: "cogito ergo sum," I think, therefore, I am.
Your own existence is something you can't go around. You can imagine yourself not existing, but the mere fact you're trying already implies your existence.
But, as we've discussed already, we can't say that about the outside world.
As we're limited to our perceptions, the outside world, exterior to our minds, could be imaginary or something entirely different than it appears to be.
Some believe we're part of a simulated reality. And for a few, we're butterflies dreaming we're people. Some of these ideas are debatable, others absurd.
But the variety of these theories indicates a lack of certainty. On the other hand, the place in which these ideas dwell (the mind) is something we can be sure of exists.
