Suppose a defense lawyer strongly suspects (to the point that he would be willing to bet a large amount of money on it) that his client has committed the crime he charged with. Would it be right or wrong for him to encourage the jury to deliver a "not guilty" verdict?

At least in the USA, the premise of the criminal justice system is that the burden is on the state to establish guilt "beyond a reasonable doubt." And there are various reasons why we might want to stick to that standard. It's not a good thing when a guilty person goes free, but it's also not a good thing when the state has low standards for establishing guilt. And so the usual idea is that everyone is entitled to a vigorous defense. Even if the lawyer believes in his/her heart of hearts that the client is guilty, the question for the judge and jury is whether the state's arguments and evidence make the case.

Is it entirely altruistic to execute a will, because any property transfer or other consequence of having (or not having) a will would not be experienced until after the testator's death?

Suppose Will writes a will, disinheriting his children out of small-minded spite and leaving all his wealth to Bill, who already has more than enough money and no significant connection with Will. Doesn't sound altruistic to me! And even though Will won't be around to watch his children's faces when the will is read, Will might well get a passel of perverse pleasure playing the scenario over in his mind while he's yet among the living. So no: exectuting a will could be an act of pure nastiness, not least because the very act of composing it has psychological consequences for the testator in the here and now.

Are there any good philosophical reasons for thinking that time travel is possible?

Yes and no. Let me explain. Some people think that is flat-out impossible. They appeal, for example, to puzzles like the Grandfather Paradox: if time travel were possible, the argument goes, I would be able to go back to 19xx and kill my Grandfather before he met my Grandmother. This would mean that I would never exist, and so the scenario requires both that I do and that I don't exist: contradiction. This is meant to show that time travel is impossible. Philosophers can help us sort through that sort of problem, and in fact some have. David Lewis's "The Paradoxes of Time Travel" (you can find it in his Philosophical Papers , volume II) is still a lucid and useful sorting of the issues. Lewis argues -- correctly, I think -- that the Grandfather Paradox doesn't show what it's meant to. Roughly, the idea is this: if I do someday travel back to 19xx gunning for Grandpa, then first, it's true even now in 2008 that there was a deranged philosopher lurking around in those days gunning for Earl Stairs. ...

Most people believe that if slavery were universally accepted, it would still be wrong. But let's suppose that, contrary to our beliefs, slavery is actually morally acceptable. Would anything be different? Surely the physical laws would be the same. Sodium would still bond with chlorine, and earth would still pull at 9.8 Newtons per kilogram. And according to the first statement, societies views do not have a casual relationship with morality. So when someone says slavery is wrong, what exactly are they asserting?

The feat of imagination here isn't quite as straightforward as it seems. Do the slaves have the same basic capacities as the slaveholders? Would the slaves vastly prefer not to be slaves? Would the slaveholders really, genuinely agree, after thinking it through, that had luck turned out so that they had been in the wrong place at the wrong time, or been born into families of slaves, it would be perfectly acceptable for them to have been enslaved? Is the practice of slaveholding generally bad for the slaves? Does it generally make their lives much more painful, fear-filled and miserable than the lives of the slaveholders? You get the drift. What makes slavery wrong, so the story would go, are various facts of the sort that the rhetorical questions above point to. In some times and places, people may have been ignorant of those facts, or may have lulled themselves into ignoring them. But chances are that anyone who was prepared to offer a defense of slavery would end up saying a bunch of...

Consider the argument: I am more than six feet tall. Therefore, I am over five feet tall. Is this a sound argument? Is it circular? Tautologous?

Let me muddy the waters in hopes that Peter will say more. According to at least some philosophers, it is simply impossible that something should contain water without containing H 2 O. If they are right, then given the notion of validity presupposed by Peter's (1), this is a valid argument: The plastic jug in my refrigerator contains water. Therefore, the plastic jug in my refrigerator contains H 2 O. But this doesn't strike most of us as a valid argument, and it doesn't help to invoke standard notions of meaning, since "water" and "H 2 O" aren't connected by meaning . One reply would be to invoke a notion of validity of the following sort: an argument is valid if there is no argument with the same logical form whose premises are true and whose conclusion is false. On that account, the little argument about water isn't valid. Needless to say, this raises tricky questions about the notion of "logical form," but it lets us honor the intuition that the water/H 2 O...

Could a big computer solve a philosophy problem?

Could a really, really smart person solve a philosophy problem? For example: could a really, really smart person "solve" the freewill problem? Some really, really smart people already have — at least to their own satisfaction. Other really, really smart people aren't convinced. Is it just that at least some of these people aren't smart enough? Or is there something else going on here? Let's consider a different example. The four-color conjecture says that using no more than four colors, any map drawn on a plane surface can be colored so that no two contiguous region have the same color. This conjecture was finally proved with the aid of a computer in the 1970s. Not all mathematicians agree that we really have a proof here, since no human being could ever check it. But we might at least say this: so long as the algorithm really was properly designed and the machine worked properly, we've got something of the same general logical sort as a mathematical proof, and we could have very good empirical...

Suppose it's your birthday, and you get your Aunt (who has an infinite amount of money in the bank) to mail you a signed check with the dollar amount left blank. Your Aunt says you cash the check for any amount you want, provided it is finite. Assume that the check will always go through, and that each extra dollar you request gives you at least some marginal utility. It seems in this case, every possible course of action is irrational. You could enter a million dollars in the dollar amount, but wouldn't it be better to request a billion dollars? For any amount you enter in the check, it would be irrational not to ask for more. But surely you should enter some amount onto the check, as even cashing a check for $1 is better than letting it sit on your dresser. But any amount you put onto the check would be irrational, so it seems that you have no rational options. Does this mean that the concept of "infinite value" is self-contradictory? If so we have a rebuttal to Pascal's Wager.

I hope that some of my co-panelists who think more about decision theory will chime in, but here are a few thoughts. Cheap first try: it seems plausible that even if every additional dollar brings some marginal utility, by the time we reach, say, a trillion trillion dollars (a septillion dollars) the utility provided by the septiliion+1th dollar is so tiny that the utility cost of worrying about it exceeds the utility it could provide. Of course, that's not really an answer to your question. What you have in mind is a scenario on which it's not just that each additional dollar adds utility, but on which the total area under the utility curve goes to infinity. But it's worth noticing that these are separate ideas. Even if each additional dollar adds value, the infinite sum might still converge to a finite number. So we can restate the problem this way: there's an infinite well of utility available, and you can choose to have any finite amount of it, but you have to specify the quantity...

Here's my challenge for those who think we have the right to sell our bodies (i.e. prostitution): Suppose Travis, a hardworking businessman who is too busy to have a romantic relationship, calls Elise, a prostitute he finds on Craigslist. Elise tells him that she would love to service him, but he'll have to wire the money in advance (she's been taken advantage of too many times). Travis complies, and the two agree to meet next Thursday night. That night Elise thinks about her career and has a change of heart. When Thursday rolls around, she comes to Travis's house and explains that she cannot go through with the act. She offers to refund the money, but Travis refuses. Travis, you see, has already invested more than the money. For one, he set aside a night for Elise that will be wasted if she leaves. And he's already accepted some risk to his reputation by contacting Elise. More importantly, Elise agreed to a contract, and contracts are not reversible on the whims of a single party. If Elise had sold...

I'm having a bit of trouble finding the argument here. Let's take a "transaction" that most of us think is just fine: accepting a proposal of marriage. If Pat agrees to marry Robin and then gets cold feet, Robin can't force the issue. But what of it? Or take another example: I agree to buy your house. I sign the contract. And then I back out. In most jurisdictions, far as I know, you can't sue me for specific performance; you can't force me to buy the house, though there are various damages that you would be entitled to recover from me. As things stand in most places, a contract for an act of prostitution isn't enforceable, and so Travis has no legal claim against Elise -- particularly if she gives back the money. But suppose that these sorts contracts were legal, since your issue is presumably with people who think they should be. In that case, there's still no reason to think that Travis has some sort of right to rape Elise, though depending on the legal regime, he might have a civil...

Can reflection destroy knowledge? Is it plausible to say that people's sense of social and moral direction can depend on not asking too many questions? Should one always justify conceptual and moral foundations of this world? Do you risk ending up in a situation where the reasons guiding your actions lose their power to guide? By demanding reasons for reasons, can reflection destroy practical knowledge?

To know something, I need to believe it. If by over-thinking or thinking unproductively I talk myself into a state of doubt, then I won't know what I formerly knew simply because I no longer believe it. Of course, if the doubts are a sort of passing intellectual vertigo, wemight well say that I really knew whatever it is all along, eventhough I had temporarily put myself out of touch with the angels of my own epistemic better nature. At least, that's the short story. The long version would get complicated and would best be provided by someone who thinks more about theory of knowledge. (And indeed... I noticed after I submitted my reply that Nicholas Smith had already given a more complkete answer a few minutes before!) But yes: there are such things as over-thinking, analysis paralysis and the like. My sense, however, is that the more common problem runs in the other direction: leaping to dubious conclusions without much of anything in the way of reflection, as Prof. Smith suggests.

We can think of a monetary system without banknotes or coins, where people would only have their money in banks, using it with credit cards and the like. Of course, there would be nothing in banks except for information on the amount of money each person would have. Now, I think that in this system there would exist nothing of which we could say "That is one euro" or "one dollar" (or whatever). But still it would be true that some people would have, say, one million dollars. My question is: if there is nothing which is one dollar, how can somebody have one dollar or a million dollars?

If having a dollar means having some thing or other, then no one could have a dollar if there weren't any. But bits of language of the sort "have a ___" often don't call for filling the blank with the name of a thing. If someone has a cold, or an idea or a worry or a lot of work to do, there isn't some thing they're carrying around in their nose or their head or have stored in their office. Unlike colds and good times, dollars once were bits of stuff and mostly still are -- at least in one sense. But having a dollar has never been simply a matter of having a bit of paper. What makes the piece of paper a dollar is that the person who has it has a certain amount of economic power, so to speak (which, by the way is another example of "having" something that's not a thing.) Money is already a lot more abstract than the creased bits of cash in your wallet let on. And so in the cashless economy you're imagining, that's what having a dollar or a euro or a million such would amount to: having what we're...

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