Does the outside world exist?

I could simply retort: How do you know that? Your reason is still about the outside world and your connection to it, and it must be based on your sensory evidence. But you can use this sensory evidence to illustrate how visual experience comes about only because you have presupposed the existence of an external world in your consciousness. But that assumption is exactly what we suspect. If you use your own impressions to prove the validity of your impressions, you're going in circles and you're not getting anywhere. If in fact everything exists only in your consciousness, would it look any different to you? It's possible that you think of these things as the real world outside of you, and that they're just a big dream or an illusion from which you can never wake up. But if that's the case, of course you can't "wake up" (as if you would wake up from a dream), because this illusion means there is no "real" world to wake up to. So it's different from normal dreams or visions. What we generally think of as dreams is that people dream of running down the street, chasing a killer lawn mower, when in reality it's all happening in their head, while they're lying in a real bed in a real house. We also think that there is something physiological going on in the brain while you sleep that causes you to dream. But isn't all of your experience a big dream, and there is no world outside of that dream? How do you know that's not the case? If you think about it, you'll see that the only thing you can be sure of is what's in your own consciousness. Everything else you believe in -- the sun, the moon, the stars, the house you live in and your neighbors, history, science and other people, even your own body -- must be based on your experiences, thoughts, feelings, and sensory impressions. That's what you can rely on directly, whether it's when you see the book in your hand, or feel the floor under your feet, or remember that Newton discovered gravity, or think that the formula for water is H2O. All but your inner experience and thoughts are far away and can only be known to you through your inner experience and thoughts. You don't usually suspect the floor beneath you, the trees outside your window, or your own teeth. In fact, most of the time you don't even think about the state of mind that makes you aware of these things. You seem to be directly aware of these things. But how do you know they exist? You could try to argue that there must be an external physical world, because if there wasn't something outside of you that shone or reflected light, that shone light into your eyes and gave you visual experience, you wouldn't be able to see things like buildings and people and stars. But I can simply retort: How do you know that? The reason you say is still about the external world and your connection to it, and it must be based on your sensory evidence, but you can use this sensory evidence to show how visual experience comes about only because you have presupposed the existence of the external world in your consciousness. But that assumption is exactly what we suspect. If you use your own impressions to prove the validity of your impressions, you're going in circles and you're not getting anywhere. If in fact everything exists only in your consciousness, would it look any different to you? It's possible that you think of these things as the real world outside of you, and that they're just a big dream or an illusion from which you can never wake up. But if that's the case, of course you can't "wake up" (as if you would wake up from a dream), because this illusion means there is no "real" world to wake up to. So it's different from normal dreams or visions. What we generally think of as dreams is that people dream of running down the street, chasing a killer lawn mower, when in reality it's all happening in their head, while they're lying in a real bed in a real house. We also think that there is something physiological going on in the brain while you sleep that causes you to dream. But isn't all of your experience a big dream, and there is no world outside of that dream? How do you know that's not true? If all your experience is only a dream, and there is nothing outside it, then any evidence you can use to prove the existence of the outside world is only part of the dream. If you tap on a table or pinch yourself, you'll hear a tap or feel pain, but that's just what's happening inside your consciousness, just like everything else. This is of no use: if you want to find out whether things in your mind can lead to the outside world, you can't rely on how they feel in your mind in order to find out. But is there anything else to fall back on? The only way you know anything is through your mind. This is true in any form: personal perception, knowledge from books, what others say, or memory. To say that there is nothing but what is in your consciousness is not inconsistent with what you are aware of. You may not even have a body or a brain at all. The reason you believe you have a body or a brain is because your senses confirm it. And you've never seen your brain, you just think everyone has a brain, so you have one. But if you have, or think you have, it's just another visual experience. Perhaps the only thing that exists is you, the subject of experience, and there is no physical world at all -- no stars, no earth, no human body. Maybe the space doesn't even exist.