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Cresswell calls this the Most Certain Principle:
MCP: if we have two sentences A and B, and A is true and B is false, then A and B do not mean the same.
Last year, I thought that this principle was most certainly false: if I say something true that is false at another world w, and somebody in w says something with the same content, then our utterances mean the same while they differ in truth value. To quote myself,
I believe that there is such a property as being two meters away. -- Not two meters away from me, or from somebody else, or two meters away from something or other. Just two meters away.
Admittedly, there is a sense in which something can be two meters away only relative to some point of reference. But compare properties like being empty and being bent. There is a sense in which, strictly speaking, persisting things can be empty or bent only relative to a time: this cup here is empty at the present time while it was full 5 minutes ago. Likewise, at least prima facie many things are empty or bent only relative to worlds: the cup is empty at the actual world, but full at other possible worlds. That's why properties are often modeled as something like functions from worlds and times to sets of objects.
...in the latest issue of Nature, some physicists published an empirical refutation of
'realism' -- a viewpoint according to which an external reality exists independent of observation.
They also advocate considering
the breakdown of [...] Aristotelian logic, counterfactual definiteness, absence of actions into the past or a world that is not [sic] completely deterministic.
As far as I can tell, what they actually found is evidence against certain local hidden-variable theories that survived Bell's inequalities. Aristotelian syllogisms and realism (in the above sense) seem to be thrown out by the principle that if you throw out the bath water, you might as well throw out the whole bathroom.
Searching. Mary is in the park, looking for Fred. She recognizes Fred's friend Ted some distance away on the left. Knowing that Fred is often in the park with Ted, she turns that way.
Waiting. Alexandre is waiting for Veronique in a cafe. He's been waiting for several hours now, and is doubtful that Veronique will ever show up. Nevertheless, he thinks it is worth waiting some more.
Mary and Alexandre are acting rationally here, even though Mary does not know that Fred is to the left, and Alexandre does not know that Veronique will ever show up. Even if it turns out that both were wrong, I wouldn't blame them for their decisions.
Sometimes, implicatures appear to survive under embedding. Take
1) the column will fail and the bridge will collapse,
which in a suitable context implicates that (the speaker believes that) the bridge will collapse as a result of the column failing. This implicature is still present if (1) gets embedded in, say, a conditional:
2) if it rains, the column will fail and the bridge will collapse;
3) if the column will fail and the bridge will collapse, you'll be in trouble.
(2) is likely to convey that if it rains, the bridge will collapse as a result of the column failing, and (3) that if the bridge will collapse as a result of the column failing, then you'll be trouble.
Reinventing broken wheels is more fun than patching small punctures in functioning ones. So here are some thoughts on desires that are undistorted by knowing the relevant literature.
It seems that unlike for rational belief, there are very few formal constraints on rational desire. For instance, if you desire A & B, it doesn't follow that you should desire A: I'd like to be beaten up and get a billion dollars compensation for it, but I don't desire to be beaten up. By the same example, you may desire A without desiring the disjunction A v B. More generally, all these principles are invalid for rational desire:
I gave a talk about the Canberra Plan on Tuesday (slides) in which I mentioned that I disagree with Lewis and Kim about the semantics of "pain": they say "pain" denotes whatever occupies the pain role in the species under consideration (or whatever is the relevant kind); I think "pain" rather denotes the property of being in a state that realises the pain role. One of the reasons I gave for my preference is that "pain" would be rather exceptional if it worked as Lewis and Kim believe.
Here is a short paper version of my GAP.6 talk "Modal metaphysics and conceptual metaphysics", to appear in the GAP.6 proceedings. It has a lot less formulas than the talk.
I distinguish two metaphysical projects: modal metaphysics and conceptual metaphysics. I show that the two projects really are distinct, and that Frank Jackson's argument for the opposite conclusion doesn't work. Then I have a closer look at how the projects come apart, and suggest that when they do, the modal project always becomes metaphysically uninteresting. Thus the term "metaphysical modality" is a misnomer: metaphysical entailment only matters for metaphysics insofar as it coincides with conceptual entailment.
I suppose I should say a little more on what I call "modal back-reference", and on the sense in which what a sentence expresses can be conceptually independent of how things are in the actual world: doesn't what a sentence express always depend on what the sentence means? Unfortunately, I don't have a simple and uncontroversial answer to that, so I just ignored this point. Hopefully no-one will notice.
I've fixed the bug where sometimes nodes in the displayed tree overlapped. I also made the proof search faster. Now Pelletier 34 is proved in only a few minutes! (Warning: the tree is huge, and might crash your browser.)
Brian argues that our intuitions about whether an action C causes somebody's continued survival is linked to the applicability of causative notions like "opening", "closing", "protecting", "threatening": if C inadvertently causes the survivor to be threatened but at the same time protects him from the threat, we are more inclined to count C as causing the survival than if C threatens the surviver but at the same time inadvertently causes him to be protected.
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