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MIT 24 0 - Lecture Notes

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. Problems of Philosophy, Fall  . / “How often, asleep at night, am I convinced of just such familiar events—that I am here in my dressing-gown, sitting by the fire—when in fact I am lying undressed in bed!” "You see all the wires going to Harry's brain? ey connect him up with a powerful computer. e computer monitors the output of his motor cortex and provides input to the sensory cortex in such a way that everything appears perfectly normal to Harry. It produces a fictional mental life that merges perfectly into his past life so that he is unaware that anything has happened to him...I'll bet you think we're going to operate on you and remove your brain just like we removed Harry's, don't you? But you have nothing to worry about. We're not going to remove your brain. We already did—three months ago!" Descartes isn’t saying that there is no external world. Maybe there is. e point is rather that even if there is an external world, we seem not to know that there is.  ,   () Knowledge of external objects is derivative; we infer their existence from the fact that we have such and such experiences. [] () Is the inference deductive? No. ere is a big gap between our having these sorts of experiences and there being something out there that the experiences accurately represent. Deductive inference guarantees its conclusion and gap that the fact that we have these experiences does not guarantee an external world. [] () Is it inductive? “Where there’s smoke, there’s fire.” No. Induction is extending an observed correlation to new cases, & this correlation has never been observed (not even once). [] () If an argument is justified, it must be justified deductively or inductively. [] () Since the inference can’t be justified deductively or inductively, it can’t be justified at all. [,,,] R Commonsense Approach: rejects the conclusion without a diagnosis of where the argument goes wrong. I am more certain that I have a hand than I am of the skeptic's premises and reasoning from those premises. Why should I give up a hypothesis I am pretty certain of in response to some philosopher's crazy argument, which contains steps I am suspicious of even if I couldn't tell you exactly why. “A typical skeptical argument is best viewed as a reductio ad absurdum of its premises, rather than as a proof of its conclusion.”. Problems of Philosophy, Fall  Naive realist: denies first step, knowledge of external objects is non-inferential or direct. Moore: “I can prove, for instance, that two human hands exist. How? By holding up two hands, and saying…’Here is one hand, … and here is another’ … now I am perfectly well aware that … many philosophers will still feel that I have not given any satisfactory proof of the point in question … ey want a proof of what I assert … when I hold up my hands and say,‘Here's one hand and here's another’ … ey think that, if I cannot give such extra proofs, then the proofs that I have given are not conclusive proofs at all...[But] I can know things which I cannot prove; and among things which I certainly [do] know are [that this is a hand].” Reductionism: allows the first step, but denies the second; there is no gap. “I have hands” is deducible from the experiential evidence, because objects are defined in terms of human experience. Scientific Approach: allows the first two steps, but denies the third, i.e., there is a gap, but it can be crossed by (a more general form of ) inductive reasoning. External objects provide the best explanation of our experience.  ,   ) Vat-stimulation is perceptually indistinguishable from reality. () ) If things are perceptually indistinguishable, I don’t know which one I am experiencing. () ) For all I know, I am a brain in a vat. (,)  It seems hard to argue with (), though it’s been tried. Mostly people take issue with ). Commonsense Approach Who made it a requirement on knowledge that one’s experience should have only one possible cause? at isn’t the way we talk. It doesn’t stop me from knowing it’s Obama that an absolutely identical twin would look the same. It doesn’t stop me from knowing it’s me that my introspective experience would be the same if it was my twin. Why should it stop me from knowing it’s a hand that hand-experiences have other possible causes? Naïve realist If it really is my hand I’m looking at, then I know; if it isn’t, then I don’t. In general, I can know something without knowing that I know it (the ‘‘ principle is rejected). () only seems plausible because we’re thinking “It’s a hand” has got to be inferred from the qualitative character of my experience. I don’t have to rule out the vat-scenario to know what is right in front of my eyes. Reductionist “It’s a hand” does have to be inferred from my experience. But that’s  because external objects are defined in terms of experience. ere’s nothing more to having a hand than systematic hand-appearances. Objects are permanent possibilities of sensation. Scientific Approach “It’s a hand” does have to be inferred from my experience. But that’s  because hands provide a more plausible explanation of that experience than vat-stimulation. Science in general proceeds by inference to the best explanation. Why not here too?MIT OpenCourseWarehttp://ocw.mit.edu 24.00 Problems in Philosophy Fall 2010 For information about citing these materials or our Terms of Use, visit:


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