Hi, what an awesome website! I have another free will related question to add to the heap! I saw an interview with Steven Weinberg, the Nobel Prize winning physicist and, I don't remember the precise phrasing, but he said something like 'I know of no law saying that nature is here to make physicists happy.' He wasn't referring to free will, but it got me thinking about something... From what I've read and heard in papers and talks (which is certainly not nearly exhaustive), it seems that their is a tendency for those who chime in on the free will issue (even professional philosophers) to approach it from the perspective that the challenge is to show that free will does not or cannot exist. What I mean is that there seems to be a tacit presumption that since we "feel" free, the burden of proof is on those who contend we are in reality not free. I understand this perspective (and it is not unique to the free will debate), but it seems to presuppose some kind of rule that says that our feelings...

As a panelist, I'm glad you like the website. Spread the word! I don't think we need to invoke feelings in order to assign the burden of proof to those who challenge the existence of free will. In the literal sense, feelings have nothing to do with it: I don't think we have reason to believe, for instance, that causally undetermined actions have a characteristic "feel" to them that causally predetermined actions lack. But neither do we have reason to believe that they don't have a characteristic feel to them. So you're right that it's only fair to leave the phenomenology -- the literal feel of our actions -- out of it. There's also the metaphorical use of "feel," as in "I just feel that human beings sometimes act freely." Feelings in that sense too are irrelevant, I think. But the reason that those who challenge the existence of free will bear the burden of proof is that pre-philosophically -- i.e., before examining the issue philosophically -- we start with a widespread set of...

In one famous trolley case, it seems clear that the driver should divert the trolley to the spur, killing one while saving five. In another, it seems clear that a bystnader should not push the fat man off the bridge, again killing one to save five in the trolley's path. But what is the justification for my intuition? Do you see any relevant, principled difference between the two cases that would explain why I should divert the trolley yet refrain from pushing the fat man?

I think it should be noted that Professor Pogge's reply invokes, or alludes to, the controversial Doctrine of Double Effect (or else something close to that doctrine). For an account of the doctrine and of some of the controversy surrounding it, see this SEP article . One problem for the doctrine emerges when we consider a reply that B2 might make: "I didn't intend the trolley to hurt the fat man. I intended only that he stop the trolley (although of course I foresaw that his being harmed would be a side-effect of his stopping the trolley). So I didn't intend harm any more than B1 did." B2's reply seems lame, no?

It has long been recognized that free will appears to be incompatible with the causality observed in the rest of the universe. There is now evidence from neuroscience that free will does not really exist. Does the fact that many people - including many philosophers - find this conclusion absolutely unacceptable constitute a manifestation of the limits of the human mind's abilities?

My diagnosis is different: I think the arguments claiming that causality (specifically, deterministic causation) rules out free will, or claiming that neuroscientific results cast doubt on the existence of free will, are bad arguments. This issue came up recently here: see the discussion at Question 4792 , particularly the reply by Professor Nahmias and the book review he links to.

I am a 16 year old and i have been asking myself the same question for a very long time but only recently was able to finally word the question.. Isnt it true that there can not be a certainty of anything outside a person's current observed world?  It still sounds very wierd but if i am sitting in a room in a building that i walked into myself, i saw all of my surrounding as i entered the building and the room. The door is closed and there is no way for me to observe anything on the outside of the room.   I can say that i know exactly what is outside that door because i saw it as i came in the room, but in reality i have zero way of being competely certain of anything i cant see or hear outside the room. I could, potentially, be in a room floating in space and have no way of knowing, givin there isnt any ovservable evidence of my location.  It may sound strange, but i believe it could be related to particle physics, etc.  The fact is that i have no certainty of anything outside my personal observed ...

I congratulate you on your interest in philosophy at the age of 16 -- in this case, your interest in epistemology (the theory of knowledge) and, within epistemology, the issue of skepticism . You posed your question in terms of certainty. I said in response to Question 4721 that the term 'certain' works in a way that allows you to be certain that some proposition P is true even though it's logically possible that P is false. But you raised a harder question: Can you be certain that P is true when the evidence you now have is the same evidence you'd have if P were false? This question is hotly debated: there are plausible grounds for answering "No" and plausible grounds for answering "Yes." You might start your investigation by reading Peter Klein's SEP article on skepticism . It's long and challenging, but I think it will reward your patience. I recommend paying particular attention to Klein's discussion of the concept of evidence. (By the way, I don't think particle...

Recently I read a newly published very short book criticisng the concept of Free Will. I thought the book made some good points and some not-so- good points, but what really disturbed me is that the author didn't ever carefully define what he meant by Free Will. Is the definition of Free Will so obvious and clear that there is no need to define it in a book intended for lay readers?

You're right to be disturbed if the author never defines 'free will' in a book criticizing the concept of free will! One frequent obstacle to progress in discussing free will is that different parties to the discussion rely on different (and often unstated) conceptions of free will. Some think of free will as whatever is necessary and sufficient on the part of an agent to make the agent morally responsible for his/her action. Some think of it as requiring the ability to have acted otherwise than one in fact acted. Some think of it as requiring the ability to have acted otherwise than one in fact acted even under the same circumstances that preceded one's action. Those conceptions of free will aren't the same -- or aren't obviously the same. It's a good question which of those conceptions, or which other conception, best fits the way we use the concept of free will (assuming we use the concept in a stable way). It's another good question how well those conceptions stand up to scrutiny. In answering...

Eddy: Nice article! I'm glad they tapped you to review Harris's book. (I too suspect that it's the book the questioner is referring to.) --Steve

What is the definition of validity under possible world semantics?

Please excuse my parentheses; I hope they don't obscure my answer. As I understand it, an inference is (deductively) valid if and only if there's no possible world in (or at) which the premise(s) is (are) true and the conclusion is false. So "Socrates is a man; therefore, there's at least one man" is a deductively valid inference, since there's no possible world in (or at) which the premise is true and the conclusion is false. Ditto for the inference "Socrates exists; Socrates doesn't exist; therefore, snow is green": Barring equivocation, there's no possible world in (or at) which the premises are both true, and so there's no possible world in (or at) which the premises are both true and the conclusion is false.

I have a question about determinism, prediction and conscious choice. Suppose we live in a deterministic universe such that some epistemically-juiced Demon could predict future events with absolute certainty long in advance. When he sits observing, he's always right about what people are going to do. But, suppose, the Demon gets a little bored decides to try to impress some humans with his gift of prophecy. He tells me that he can predict any of my actions: for example, what I'm about to eat for lunch. He gives me an envelope and tells me to open it after I've made my lunch. I do and he's right about the sandwich I was just about to bite into. But at that point can't I just as well change my mind and eat something else? And isn't that true no matter what prediction is made, provided I'm aware of it sufficiently in advance of its "coming true"? Of course, the Demon could have made auxiliary predictions about how his telling me would affect my choice. And those could be true. But if I'm privy to...

Could you or the Demon even understand what he tells you? The Demon tells you (a) that he has predicted what you'll eat for lunch. Of course, now that he's told you that, what he's really told you is (b) that he has predicted what you'll eat for lunch given that he's told you (a). Notice that (b) isn't the same item of information as (a). But wait. If he's told you (b), then really what he's told you is (c) that he has predicted what you'll eat for lunch given that he's told you (b). Notice that (c) isn't the same item of information as (b) or (a). And so the regress continues, forever. Therefore, I wonder if anyone can understand the story you've sketched well enough to see what the story implies or what's consistent with it. In this article , my co-author and I raised a similar worry in regard to Newcomb's problem, a famous problem in rational decision theory that also involves a predictor. But I'm not sure anyone else was convinced by our argument! In any case,...

is reason infallible? can reason alone help us understand everything about all aspects of humanity and life?

Your questions are so terse that I can't be confident I'm interpreting them as you intended. But I'm inclined to answer them "Yes" and "Yes." If by "reason" you mean "deductively valid reasoning," then reason is infallible in the sense that it's guaranteed never to lead us from truth to falsity. Even so, however, we're fallible in our use of reason: we can think that some bit of reasoning is deductively valid and be mistaken about that (within limits: some reasoning is so basic that it would make no sense to think we could be mistaken about its validity). Still, deductive reasoning differs from other ways of forming beliefs in that when it's properly employed it can't lead us into error. Can reason alone help us understand everything? Yes, with emphasis on help . We can apply deductive reasoning to the inputs we get from our senses, from introspection, from memory, from our traffic in concepts, etc., to see what those inputs imply, to see what their content is, to understand them...

Even if there is overwhelming evidence in opposition of solipsism, it still cannot be disproven to 100% certainty. Is it just the nature of any conscious entity to have to have faith in their surroundings being external and objective to the mind, while still viewing them subjectively, in order to just live their lives? Or can one really live their entire life suspecting solipsism?

I'd question your assumption that solipsism "cannot be disproven to 100% certainty," unless by "disproven to 100% certainty" you mean "shown to be logically impossible," but in that case I'd question your use of "disproven to 100% certainty." I think the latter phrase, or something close to it, has a use in our language, and therefore a conventional meaning, and its meaning isn't the same as "shown to be logically impossible." That is, I think we use the phrase in such a way that something can be disproven to 100% certainty without being shown to be logically impossible. Furthermore, although they don't quite convince me, some argue that solipsism can be shown to be logically impossible because it requires the existence of a "private language," something that's allegedly incoherent. For (much) more on that argument, you might start with this SEP article .

Our understanding of the physical universe is better than say, what it was a few thousands of years ago. We may continue to understand it better as time progresses. My question is, would it at all be possible, at some stage, to say that we know it all, that the universe has been stripped naked and it no longer holds any more mysteries?

I strongly doubt it! I think it's a very good bet that we human beings will continue to improve our understanding of the universe, but I strongly doubt that our understanding will ever become perfect, that there will come a time at which we've answered every meaningful question about it. Certainly there's no evidence from the history of science that such a day will come. Quite the contrary. Every time scientists have thought that the end is in sight, that soon no further important questions would remain in some domain, a revolution has occurred to open unforeseen avenues of inquiry. Here's a trivial reason why the possibility of further inquiry won't end. Suppose we answer the 'final question'; call it 'FQ'. Why did we ask FQ? That question is meaningful and has to be distinct from FQ. Call it 'FQ*'. Why did we ask FQ*? And so on. A less trivial reason stems from the widely held assumption that at least some aspects of our universe are contingent rather than absolutely necessary. If...

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