Theory of Knowledge: New Responses to Skepticism

my name is Jennifer Nagel I teach philosophy at the University of Toronto and today I want to talk to you about several new ways contemporary philosophers tackle the problem of skepticism this video covers three different proposed solutions to the skeptical problem the first two are semantic or meaning based approaches and the third is a strategy will call the defensive approach the first semantic Theory will look at comes from Hilary putnams book reasoned truth and history one of putnams goals in the book is to show that skepticism ultimately self destructs the words that the skeptic is using can't really have the meaning but the skeptic needs them to have in order to make you feel like you don't know anything about the outer world the skeptic needs to use meaningful language to describe a scenario that might for all you know actually be your reality Putnam argues that if we take a closer look at what makes our words meaningful will see that the skeptic can make his scary scenario meaningful only in a situation where that scenario couldn't be what's really happening to you to explain putnams semantic treatment of skepticism we'll need to start with a look at his general semantic theory Putnam is an advocate of a position known as semantic externalism described in more detail in the Wi-Fi video on meaning and language according to semantic externalism what gives your words meaning isn't a matter of your inner ideas or psychological states but rather your relationship to things in your environment for example to use the word water meaningfully you don't need to have an accurate scientific theory of what that substance really is even people with very different ideas can be talking about the same thing when they use that word imagine the sentence I want a drink of water said by a young child a medieval peasant and a chemistry professor they can all meaningfully use the word water because they've had the right kind of contact with the substance itself not because they all share the same ideas about its nature for semantics external ists even secondhand contact can make something meaningful for you you may not have been to Mount Everest yourself but if you've seen photographs and heard stories from people who have been in contact with the mountain then the expression Mount Everest can have meaning for you let's think about the skeptics brain-in-a-vat hypothesis assuming for a minute that we're in the ordinary physical world of common sense our word brain is meaningful because we've seen brains in jars at the anatomy museum in TV documentaries about brain surgery and our word that is meaningful because we've handled real vats large buckets holding olives at the supermarket or Greece in an industrial kitchen we can meaningfully imagine what it would be like for a brain like the one from the museum to end up in a vat like the one from the supermarket now imagine everything from a new perspective think about how things look from the perspective of poor Brian who is now and has always been a brain-in-a-vat whose entire sensory experience has been generated electronically by his supercomputer if Brian uses the word VAT what does he mean Putnam thinks that if Brian has never been in contact with anything but computer-generated electronic simulation his word VAT just refers to some patterns in that simulation or maybe to the computer program generating those patterns Brian has never handled a physical VAT or seen one or even spoken to someone who's seen one he's just been using that word to respond to certain computer-generated sensations that's the reality of his environment and the place where his words get their meaning likewise Brian's word brain doesn't mean a physical organ with real blood vessels and tissue he's never encountered one of those inside his simulation when he's used the word brain he been encountering elements in his computer-generated virtual reality that anatomy museum he remembers visiting is really just a pattern of sensations electronically generated by the computer he's hooked up to Brian has no access to physical brains or vats stuck inside his virtual reality he can only experience and use words to pick out elements of that environment according to Putnam Brian doesn't have the semantic resources to describe or understand the situation he's in real brains and vats are one level up from the reality that Brian is experiencing meanwhile in the common sense world we can grasp the meaning of the sentence someone could be a brain-in-a-vat in the way the skeptic wants us to if we've had the right kind of contact with physical brains and vats but if we've had that kind of contact with brains and bats then we aren't just stuck in a virtual reality we're in the common-sense world and the skeptic shouldn't scare us critics have raised many worries about putnams proposed semantic solution to skepticism not everyone accepts his semantic externalism and even those who do have pointed out that there's at least one way that the skeptic could easily create meaningful doubts Putnam focuses on the situation of a brain-in-a-vat who's never been acquainted with the outer world but what if you did know the outer world until midnight last night when you were kidnapped by an evil scientist and invited so your experience right now is a computer-generated illusion right now your words brain and that still have their ordinary real-world meanings anchored in your past experience in real anatomy museums and supermarkets so you can meaningfully worry about being a very recently installed brain-in-a-vat whose experiences are now all deceptive even if semantic externalism is the right theory of meaning the skeptic can still make us worry about what we know there's a newer version of the semantic approach that takes a much more cheerful path rather than trying to show that the skeptics threats can't be meaningfully true David Chalmers argues that the skeptics threats aren't really very threatening Chalmers observes that the skeptic uses global skeptical scenarios like the brain-in-a-vat hypothesis to try to make you fear that most of your everyday beliefs are false what Chalmers thinks however is that most of your everyday beliefs are true even if you are a brain-in-a-vat sure Bryan's living inside a virtual reality but he has lots of true beliefs about that environment Bryan's beliefs are about things that are ultimately computational in nature but that's a point about the underlying metaphysics of Bryan's world not a point about the everyday level of his beliefs if you believe that you're looking at your hand touching a computer keyboard then this belief can equally well be true whether you're in a common-sense world looking at an ordinary physical hand or in a brain and of that scenario looking at an image generated by the supercomputer in the brain and of that scenario your word hand means something that people outside the bat would call a virtual hand or a simulated hand but it's the only kind of hand you're acquainted with and it's what you mean by the word hand when you say my hand is on the keyboard you've said something true about your reality discovering that reality is ultimately a big computer simulation is a bit like discovering that string theory is true maybe reality is weirder than we originally thought it was but such discoveries don't undermine all our everyday knowledge we can still know that we have hands and that there are olives for sale at the supermarket whether these hands and supermarkets are ultimately made of particles vibrating one-dimensional strings or instructions in a computer program on this view sceptical scenarios don't really threaten most of the knowledge we care about there are many other ways of trying to address the threat of skepticism the last one we'll look at here is the defensive approach this approach starts by recognizing that the skeptic is a very tricky opponent ordinarily when we try to persuade people of something we try to build an argument starting from premises they will accept if the committed skeptic is going to raise doubts about all possible premises then he'll be hard to attack instead of trying to convince the skeptic that he is wrong advocates of the defensive approach start from a common-sense worldview and try to explain why skepticism ever seemed attractive in the first place perhaps there's something wrong with some of the natural intuitions that made skepticism seem appealing and if we can explain what is wrong we can resist the appeal Timothy Williamson suggests that skepticism can seem appealing because it's anchored in a generally helpful ability of ours our ability to suspend judgment and double-check our thinking on any given point is like a cognitive immunity system it can increase our confidence in things we've figured out well while helping us purge inconsistencies and mistakes skepticism in his view is like an autoimmune disease in which this good thing is carried too far and ends up destroying itself if we suspend judgment on too many points all at once then we won't have the resources we need to figure out what's worth holding on to advocates of the defensive approach try to identify the factors that made skepticism look appealing one possible factor is that the skeptic somehow leads us into making some kind of mistake about what knowledge is maybe the skeptic challenges us to provide a decisive argument for something we believe and some psychological quirk makes us feel that we can't know something unless we can produce a decisive argument for it if decisive arguments aren't really required for knowledge however then the skeptic is misleading us so one way to build up our defenses against skepticism would be to get a better picture of what knowledge itself really is the next few videos in this series take a closer look at positive accounts of the nature of knowledge you you