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Dear philosophers: In my reading of Descartes's Discourse on Method, I am fascinated by his project of universal doubt and the promise it seems to give to eliminate the many presuppositions we have. However, it seems that Descartes meant whatever belief one has is not justified if it can be subjected to any doubt, including skepticism. Therefore it would seem that answering skepticism should be among the priority in philosophical research. But this is a very strict requirement - is it the case in current philosophy research? If not, how do philosophers justify not making it the priority?

Three points: 1. It's not clear that the project of eliminating all of our presuppositions even makes sense. For instance: Could we coherently try to eliminate our presupposition that eliminating a given presupposition is inconsistent with keeping that presupposition? I can't see how. Indeed, Descartes himself seems ambivalent about the possibility, or desirability, of eliminating all of our presuppositions, because in his work he frequently appeals to unargued-for principles that, he says, "the natural light" simply shows us must be true. 2. Your argument for the claim that "Answering skepticism should be [a] priority in philosophical research" relies on this premise: Descartes was correct to claim that no belief is justified if it can be subjected to any doubt. Most philosophers, now and in Descartes's time, would reject that condition on justified belief as far too strict. They would challenge Descartes to derive that strict condition from a recognizable concept of justified belief, rather...

What do you think is a satisfactory response to external world skepticism? I'm having a hard time finding one I can accept.

The external-world skeptic purports to show that I can't know any external-world proposition P. How about this response? 1. Conceptual analysis reveals that knowledge is nothing more than reliably produced true belief, where reliability falls far short of logical infallibility. 2. If knowledge is nothing more than reliably produced true belief, then the skeptic's sensitivity condition on knowledge is false: I can have a reliably produced true belief of P, and hence knowledge of P, even if I would falsely believe that P if I were being deceived by an evil demon. (Analogy: My gas-engine car can be reliable even if it wouldn't work at all if it were on the airless surface of the moon.) 3. In particular, I can have a reliably produced true belief, and hence knowledge, that I'm not being deceived by an evil demon even if, were I being deceived by an evil demon, my belief that I'm not being deceived would not be reliably produced. The skeptic then predictably asks: "But how do you know that...

Doesn't trying to demonstrate how we know anything beg the question?

It needn't. Like Descartes, you might try to demonstrate a priori that you possess perceptual (i.e., external-world) knowledge. Your demonstration needn't presume perceptual knowledge in the course of demonstrating that you possess perceptual knowledge. Therefore, your demonstration needn't beg the question of whether you have perceptual knowledge in the first place. Most philosophers, I think, regard all such demonstrations (including Descartes's) as failures, but I don't see any reason to think that all such demonstrations must fail because they beg the question. Consider a more interesting case. Suppose I analyze knowledge as true belief produced by a reliable mechanism , i.e., a mechanism that yields far more true than false beliefs in the conditions in which it's typically used. A skeptic then challenges me to show that some perceptual belief I regard as knowledge, such as my belief that I have hands, was in fact produced by a reliable mechanism. In response, I offer empirical...

Hi! I wonder what "knowledge" is. I heard the JTB argument that says knowledge must be a justified, true belief. Then there is the Gettier problem in which JTB is not sufficient to describe knowledge. But I suppose, to say that "JTB is not enough for knowledge", one must have a definition of knowledge in the first place which is not "justified, true belief". So I was so curious what the definition of knowledge, about which philosophers have been discussing so long, actually is?

You're right that according to the JTB analysis of the concept of knowledge (it's really an analysis rather than an argument), propositional knowledge is identical to justified, true belief. Gettier cases, as you say, are meant to show that knowledge requires more than justified, true belief. But Gettier cases don't proceed by assuming a different analysis (or definition) of knowledge than the JTB analysis: if they did that, they would be guilty of begging the question against the JTB analysis. Instead, Gettier cases involve scenarios in which intuitively the subject lacks knowledge of a proposition despite having a justified, true belief of the proposition. We're supposed to agree that, intuitively, Smith doesn't know the proposition Jones owns a Ford or Brown is in Barcelona , even if we don't have in mind any specific definition of "knowledge." Compare: If I propose an analysis of the concept of a lie on which a lie is nothing more than a false utterance, you can refute my analysis by...

My question relates to reclusive behavior. I wish not to be active socially because it requires so much time and I seem not to learn or be entertained by the contact with others. I am 83 years old and was a medical sales person throughout most of my life. I am a widower. Most of my time is spent on the internet learning things I have wondered about throughout life. My question is: Do very socially active people have less interest in learning things they do not know or do they already know or understand all that they ever wondered about. All information that may be provided regarding my inquiry will be appreciated.

The reclusive behavior you describe will be familiar to many philosophers! The great Scottish philosopher David Hume (1711-1776) famously wrote that socializing with friends helped him escape from his philosophical brooding when he felt overwhelmed by it. But thank goodness for his philosophical brooding! Otherwise he'd have been a much less important contributor to human civilization. You've asked a psychological question, really, so I'm not equipped to answer it, but the list of philosophers who have preferred thinking over socializing is long and illustrious. I'd recommend that you look for psychological literature that discusses the personality traits of introversion and extroversion and their characteristics. If you should discover that extroverts typically "have less interest in learning things" or believe "they already know or understand all that they ever wondered about," then how sad for them. Keep inquiring!

Can we unknow what we already know?

I'd say yes . One way would be if (for whatever reason) you ceased to believe some proposition P that you formerly knew to be true. If belief is a precondition for knowledge, then you'd no longer know that P. Another way might be, while retaining your belief of P, to come to believe (or indeed even know) some proposition Q your belief of which undermines your justification for believing P and thereby deprives you of the knowledge of P that you formerly had. See Carl Ginet's article "Knowing Less By Knowing More" (linked here ).

I had a brief chat with a work colleague today about the nature of reality and our perception of it. Essentially, his contention was that because we all basically agree on our external physical reality (e.g. when I hand him a cup of tea we both agree that I've just passed him a cup of hot tea), there must be an external reality because we both seem to agree on what it's like. If there wasn't such an external reality and we didn't essentially agree on it, he pointed out, we wouldn't be able to even ask for a cup of tea because my idea of what a cup of tea actually is would be totally different (or at least different enough to make meaningful communication difficult). Therefore, he concluded, it's common sense that we must be talking about and looking at the same "real" things and that we both experience them in the same -- or very similar -- way. Age-old philosophical problem solved! But it can't be that simple. So my question is what are the main problems with this "consensus" view of reality? Or, to put...

I've seen only one of the Matrix films, the first one. You might ask your colleague how he can be certain that things in our world aren't as they're portrayed in that film: that is, you and he merely believe you're conversing in the ordinary way about an ordinary teacup, when in fact you're both hooked up to a computer that's simulating the conversation, the teacup, and your surroundings. Is there some internal indication, something about the way things feel to him during such a conversation, that rules out a Matrix-style simulation? What could that be? Granted, neither you nor your colleague are at all inclined to believe that you're living a simulated existence, but that's just how the Matrix wants it!

In the light of the current state in philosophy, do skeptics still get an upper hand? Can we really know anything with certainty?

I'm going to refer you to two websites. At the PhilPapers Survey , you'll discover that only 4.8% of "target faculty" said that they accept or lean toward skepticism. Among specialists in epistemology (the theory of knowledge), that figure increases to 9.4%, but it's still small enough to suggest that philosophers in general don't think of skepticism as having the upper hand once the reasons for and against it are examined carefully. For detailed discussion of your second question, you might start with the SEP entry on "Certainty" . I hope you find these resources helpful.

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