I don't think that such an argument would rationally compel external-world skeptics (who say that no one can know that there's an external world) to abandon their view. External-world skeptics think that no one can know that solipsism is false, where solipsism is the claim that nothing external to oneself and one's mind exists. The solipsist won't grant that geometry consists of truths that are independent of his own mind, because he thinks nothing is. The solipsist could admit that his perceptions have a geometric character to them without having to attribute that character to something external. So I don't think solipsism can be disproven in the way you suggest. All of this assumes that solipsism is otherwise intelligible. But one might argue that solipsism is unintelligible because it relies on the incoherent idea of a 'private language', an idea explored in detail in this SEP article .

You take issue with the way the content of the man's belief is being described in this case: you suggest that the content of his belief is the more specific (1) 'There is a sheep 200 yards out there' rather than the less specific (2) 'There is a sheep out there'. If we're worried about the actual content of the man's belief, then (1) strikes me as unrealistically specific: 200 yards rather than 201 yards? But never mind that. We can easily use (1) to generate a Gettier case: suppose that the man validly deduces that (2) from his belief that (1) and thereby comes to believe that (2). Valid deduction is one way in which we come to believe things. If he's justified in believing that (1) even though (1) is false, then presumably he's justified in believing that (2) by validly deducing (2) from (1). So he's justified in believing that (2), and (2) is true because of a sheep he can't see. So he has a justified, true belief that (2) yet doesn't know that (2).

Translating the argument into symbolic terms quite literally, we get this: 'If F, then R. Not F. Therefore, not R.' That form of argument does indeed commit the fallacy of denying the antecedent: the premises don't logically imply the conclusion; the truth of the premises doesn't logically ensure the truth of the conclusion. The first premise says that F is sufficient for R; it doesn't say that F is necessary for R. In that case, R can obtain even if F fails to obtain. My hunch is that you're interpreting 'If F, then R' as 'R if and only if F': you're interpreting the conditional as a biconditional , i.e., as the claim that F is both necessary and sufficient for R. 'R if and only if F' and 'Not F' together imply 'Not R'. Your interpretation is understandable, because conversationally we often do intend to assert a biconditional when we use conditional language. A parent's 'If you clean your room, you can watch TV' usually means 'You can watch TV if and only if you clean your room...

From what I can gather, you're treating 'consciousness' as synonymous with 'soul'. You write, "as part of the content of consciousness: that is, of the soul." But 'soul' is a much more loaded term than 'consciousness': people tend to use 'a soul' or 'the soul' to denote a metaphysical substance , as Descartes did, whereas they tend to use 'consciousness' to denote an activity , a property , or a state of some substance, even if the substance is a material one. So I think it's better to use the less loaded term 'consciousness' when talking about what it is that we directly experience. I agree that it's hard to deny the existence of one's own consciousness, but there are philosophers who (claim to) deny it. They're discussed in this entry from the SEP (see especially section 3.3). It's a challenging article but worth the effort, I believe. I hope it's helpful. But let me emphasize that one can accept the existence of one's own consciousness without accepting the existence of what's...

You asked: "Could the issue be a conflict of opposing moral principles that may just be forever unsolvable by rational argument? So maybe you just can't produce arguments that can 'bridge the gap' between the two sides, i.e., the arguments just don't exist that would have the rational force and traction against the other side." I don't see it as a conflict of opposing moral principles. I think each side sees itself as trying to work out the implications of our shared concept of moral responsibility . One side thinks that our shared concept requires indeterminism; the other side thinks it doesn't. Or maybe our shared concept is inconsistent in both requiring and not requiring indeterminism, or we have two distinct concepts of moral responsibility, but even that I wouldn't classify as a conflict of moral principles. In any case, I'm not pessimistic about the possibility of making progress in this debate. Indeed, I think we've made progress in the last several years and will continue to. The new field of...

Prof. Smith gave a detailed and honest answer to which I don't really have anything to add. But two things about your question struck me. First, your GRE scores seem to combine two different scales: the current scale on which Analytical Writing is scored out of 6 and the old scale on which Verbal and Math (Quantitative) were scored out of 800. Nowadays, Verbal and Quantitative are scored out of 170. Did you take the GRE on different occasions separated by some years? In any case, an Analytical Writing score of 6 is 99th percentile, as is a Verbal score of 780. Those scores should impress anyone who sees them. Second, I'm struck by your having published a book on philosophy and skepticism before even entering a doctoral program. I'd be surprised if any of your competitors have done that. If the book is good and the publisher is reputable, you'll certainly stand out from the crowd. My only concern in that case would be whether you think you still have much to learn about (say) skepticism...

It would be helpful to know which answers on the site you're referring to, but I'll take a stab at your question anyway. The only difference between your formulations (a) and (b) is the second disjunct in each, so I'll focus on that. I presume A is some statement. What's the difference between "Not A is true" and "A is not true"? I'm not sure there's always a difference. Depending on the system of logic or semantics, "Not A is true" can mean merely (i) "Whatever truth-value (if any) A has, it's not the value true ." Or it can mean (ii) "A is false " in systems in which every statement is true or false. The difference between (i) and (ii) is sometimes important, such as when we're dealing with the classic Liar sentence (L) "This sentence is false." One might say that L is not true and yet not false either: one might say that L is neither true nor false.

I presume you're asking a normative or conceptual question, rather than a descriptive question about how healthcare systems are in fact viewed or implemented in various places. I'd answer, then, that whether ethical principles are objective or relative, universal or particular, doesn't depend on the subject matter at hand. If ethical principles depend on the place or culture (like rules of etiquette), then it seems they must be relative no matter whether they concern the ethics of healthcare or (say) the ethics of meat-eating. On the other hand, if ethical principles are true or false objectively (like statements in chemistry), then it seems they must be true or false objectively regardless of the subject matter. I can't see how there could be objective principles concerning the ethical permissibility of eating meat but only culturally relative principles concerning the ethical permissibility of aborting a fetus or euthanizing a patient. This isn't to say that objective and universal principles of...

Hmm. I can't tell whether your answer engages the timeless question. But I think the timeless question is deeply problematic anyway, as I explain in my contribution to Tyron Goldschmidt's new edited collection of essays on the topic. You seem to be saying that if there were nothing, then at least the following question would exist : "Why is there nothing rather than something?" (or, perhaps more properly, the question expressed in the actual world by the string of English I just quoted). In that case, it's impossible for there to be nothing. I suppose it's open to the timeless questioner to reply that questions don't exist independently of languages and hence independently of language-users, in which case the question wouldn't exist if there were nothing (else).

You asked, "What I really want to know is does something exist simply because someone can think of it and see it in their mind, or does it have to be seen, touched or smelled in the physical world?" I'd say neither . There's a sense in which I can think of a unicorn and see it in my mind: I can imagine it. But my feat of imagination doesn't show that unicorns exist. I can have an idea, or an image, of a unicorn, and perhaps then my idea or image exists. But that doesn't show that unicorns exist, because my idea isn't of an idea, and my image isn't of an image; instead, it's an idea, or image, of a unicorn. On the other side, physicists tell us that neutrinos exist, but it's at best a stretch to say that neutrinos can be seen or touched, much less smelled! And it may well be that abstract objects such as numbers exist even though we can't see, touch, or smell them.