Descartes then imagines the following possibility. How do I know that I'm not dreaming right now? I seem to be sitting in a dressing gown in front of a pot belly stove in which there is a nice warm fire going. I've got my parchment and I've got my quill pen and I'm trying to do some writing, but I've had dreams like this before. Maybe I'm having a dream right now in which I'm just having a vivid experience of doing the things that I think I am, but in fact I'm lying in a bed somewhere snoring away. Descartes says, make sure I know how to rule that out. He does make one point, which is a bit of sort of a suggestion. He tips his hand a little bit and show the reader where he's going. He mentions that even in dreams, those dreams need what he refers to as raw materials. For example, idea of extension, how big an object is, shape, quantity, size, number and location. And you suggest that those are the ideas that will end up having some role to play in a positive story that once to give of the nature of the knowledge. But he says at this point, I can't be sure, I'm just going to sort of suggest the direction might be going, but I'm not, we still have to earn our right to get there. But it seems on the face of it that things like geometry and arithmetic are more certain than, for example, astronomy and medicine. Because geometry and arithmetic seems like the things that I can do in the privacy of my own thoughts, in this a priori way that we mentioned before. Whereas, for example even though astronomy and medicine seem like they're sciences they still require some claims about the world outside of our minds. And maybe those claims can be mistaken if we're being deceived in some way by virtue of hallucinations, something of the kind. To take Descartes skepticism in a more contemporary form consider the following hypothesis. Imagine this guy, let's call him Zeke, a neuroscience graduate student, who's nevertheless one of the world's leading experts on how to stimulate somebody's brain. In such a way as to produce experiences. Now suppose that one night, under the cover of darkness, he and couple of his associates sneak into a dorm room or apartment building where you're sleeping. And they etherize the room in such a way as to cause you to go unconscious and they pull your body out. They steal under cover of darkness, sneak you back into the underground lab where Zeke has all of his gizmos. And they carefully, painstakingly remove your brain and parts of your essential nervous system from your body. And then put it in a vat of electrochemical conducing fluid causing it to float there, and now what Zeke and his associates are able to do is send electrochemical signals through that fluid. In such ways to stimulate your neurons in various ways. And Zeke has been following you around, so have his cronies. They have been following you around, so that they know what your schedule is like, they know who you send messages to via text. They know who you get phone calls from. They know about what types of shows you like to watch on your computer, or on TV. What YouTube channels you subscribe to, etc. They know what your daily routine is more or less like, so that when 7:15 in the morning comes by, that's when you normally wake up. Instead you're lying in bed being woken up by your alarm clock, because you're not in bed anymore. They say okay, now it's time to stimulate this person with the experience of being bothered by an alarm clock, and now it's 7:22. The experience of rolling out of bed and putting on some slippers. 7:27, the experience going downstairs to their kitchen or the dorm cafeteria, whatever it is, getting some food. And likewise, they simulate experiences throughout your day that were just like the ones that you would normally have in the course of a typical day in your life. They might even simulate experiences if you're sitting in a library reading a book of philosophy, they can do that. After all, if your brain is just something that produces electrochemical stimuli in such ways to make you have thoughts, make you have experiences, then perhaps that's something that at least is in principle possible, even if right now we don't have all of the technology that we need to do that. But if it's in principle possible, then Descartes wants you to ask yourself: how do you know that's not happening to you right now? How do I know that last night in my sleep, Zeke and his friends or some local analog of them, didn't sneak into the place where I was sleeping? Etherize me, knock me out, and then drag my body out of where I was, take it down to the lab, remove the brain from my body, etc, and now here I am. I think that, you might say to yourself, I think that I'm sitting in a library or a cafe, with my tablet, or laptop, watching a lecture on philosophy. But maybe what's happening is that I'm having my brain stimulated by Zeke and his cronies in such a way as to make me think that I'm having that experience. But in fact, it doesn't represent anything outside of my mind. What can you do to rule that out? You might say well, I can pinch myself or I can even take a knife and cut myself, make myself bleed a little bit. I'm not suggesting that you do that, but you might think that's a possibility. But that if you reflect on it, notice that Zeke could make you have that experience as well. That is to say, Descartes will point out that there's nothing right now, at least that he can think of, that could do to determine conclusively that you're not in that brain in a vat type of a experience. Nothing you can do to show yourself conclusively that that's not what's going on. But if you can't rule that possibility out, then how can you say that you know that you are sitting in a chair at a library, or a cafe, or on your couch at home. Or wherever you might happen to think that you are. Any experience you have right now seems to be consistent with the possibility that your brain and central nervous system are floating in Zeke's vat, being stimulated in various ways. By his electrochemical impulses, even though you feel sure that that hypothesis is not true. Descartes might say maybe that's just a prejudice on your part that you need to give up if we're going to have any chance of providing a new foundation for the sciences, and getting what we take to be knowledge, to be genuine knowledge and not just seeming knowledge, not just apparent knowledge. Those of you who've seen the movie, one of the series of the Matrix movies will now realize that the screen writers to that movie just basically went to the philosopher library. And stole a lot Descartes ideas in order to make the movies, I'm not taking anything away from the quality of the movies, but the ideas there, the idea that you, for all you know could be a being that's spends all of its time inside of an energy producing pod producing energy for malevolent machines is just their take on the original Cartesian idea of what we now refer to as ''Radical Skepticism''. So Descartes wants to say that right now, I don't know that I can be certain of anything. He writes, whether I'm asleep or awake maybe it's true that two and three make five and a square doesn't have more than four sides. It doesn't seem possible to such obvious truth to be subject to the suspicion of being false. But on the other hand, I do judge that sometimes others make mistakes in matters that they believe they know most perfectly. How do I know that I'm not in a similar fashion being deceived every time I add two and three, or count the sides of a square? So by the end of Meditation I Descartes says, I sometimes find for a moment that I feel that I know something about what's going on with myself. But maybe that's kind of like a prisoner who enjoyed imaginary freedom during his sleep. Somebody's in prison who has a dream in which he's running free and unshackled through a field of flowers, but then I wake up from that dream and realize that no I'm still stuck in this cell. Descartes says well, yes given that perhaps depressing realization, maybe I've got to admit that the possibility that nothing is certain, maybe I just have to think of myself as being in a whirlpool. In which I have no ideas as to how to go up or how to go down. Maybe I've got to give up all my knowledge, and I'm at a loss to figure out how to get back any.
