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An evil scientist might have built a brain in vat that has all the experiences you currently have. On the basis of your experiences, you cannot rule out being that brain in a vat. But you can rule out being that scientist. In fact, being that scientist is not a skeptical scenario at all. For example, if the scientist in question suspects that she is a scientist building a brain in a vat, then that would not constitute a skeptical attitude.
Decision theoretic representation theorems show that one can read off an agent's probability and utility functions from their preferences, provided the latter satisfy certain minimal rationality constraints. More substantive rationality constraints should therefore translate into further constraints on preference. What do these constraints look like?
Here are a few steps towards an answer for one particular constraint: a simple form of the Principal Principle. The Principle states that if cr is a rational credence function and ch=p is the hypothesis that p is the chance function, then for any E in the domain of p,
In On the Plurality or Worlds, Lewis argues that any account of what possible worlds are should explain why possible worlds represent what they represent. I am never quite sure what to make of this point. On the one hand, I have sympathy for the response that possible worlds are ways things might be; they are not things that somehow need to encode or represent how things might be. On the other hand, I can (dimly) see Lewis's point: if we have in our ontology an entity called 'the possibility that there are talking donkeys', surely the entity must have certain features that make it deserve that name. In other words, there should be an answer to the question why this particular entity X, rather than that other entity Y, is the possibility that there are talking donkeys.
Noam Chomsky's New Horizons in the Study of Language and Mind contains a famous passage about London.
Referring to London, we can be talking about a location or area, people who sometimes live there, the air above it (but not too high), buildings, institutions, etc., in various combinations (as in 'London is so unhappy, ugly, and polluted that it should be destroyed and rebuilt 100 miles away', still being the same city). Such terms as 'London' are used to talk about the actual world, but there neither are nor are believed to be things-in-the-world with the properties of the intricate modes of reference that a city name encapsulates. (p.37)
I don't know what Chomsky is trying to say here, but there is something in the vicinity of his remark that strikes me as true and important. The point is that the reference of 'London' is a complex and subtle matter that is completely obscured when we say that 'London' refers to London.
Every now and then, I come across a link to a paper on academia.edu that looks interesting. I myself don't have an account on academia.edu, and I don't want one. This means that in order to look at the paper, I have to go through the following process.
As you can imagine, I rarely go through all that hassle. Usually I look around if I can find the paper somewhere else and give up if I can't.
Given some evidence E and some proposition P, we can ask to what extent E supports P, and thus to what extent an agent should believe P if their only relevant evidence is E. The question may not always have a precise answer, but there are both intuitive and theoretical reasons to assume that the question is meaningful – that there is a kind of (imprecise) "evidential probability" conferred by evidence on propositions. That's why it makes sense to say, for example, that one should proportion one's beliefs to one's evidence.
In 2008, I wrote a post on Stalnaker on self-location, in which I attributed a certain position to Stalnaker and raised some objections. But the position isn't actually Stalnaker's. (It might be closer to Chisholm's). So here is another attempt at figuring out Stalnaker's view. (I'm mostly drawing on chapter 3 of Our Knowledge of the internal world (2008), chapter 5 of Context (2014), and a forthcoming paper called "Modeling a perspective on the world" (2015).)
In "Ramseyan Humility", Lewis argues for a thesis he calls "Humility". He never quite says what that thesis is, but its core seems to be the claim that our evidence can never rule out worlds that differ from actuality merely by swapping around fundamental properties. Lewis's argument, on pp.205-207, is perhaps the most puzzling argument he ever gave.
Lewis begins with some terminology.
In The Logic of Decision, Richard Jeffrey pointed out that the desirability (or "news value") of a proposition can be usefully understood as a weighted average of the desirability of different ways in which the proposition can be true, weighted by their respective probability. That is, if A and B are incompatible propositions, then
(1) Des(AvB) = Des(A)P(A/AvB) + Des(B)P(B/AvB).
So desirabilities are affected by probabilities. If you prefer A over B and just found out that conditional on their disjunction, A is more likely then B, then the desirability of the disjunction goes up. That seems right.
Superficially, modal auxiliaries such as 'must', 'may', 'might', or 'can' seem to be predicate operators. So it is tempting to interpret them as functions from properties to properties: just as 'Alice jumps' attributes to Alice the property of jumping, 'Alice can jump' attributes to her the property of being able to jump, 'Alice may jump' attributes the property of being allowed to jump, and so on.
Perhaps the biggest obstacle to this approach comes from quantified constructions. If 'Alice may jump' attributes to Alice the property of being allowed to jump, then 'one of us may jump' should say that one of us has the property of being allowed to jump. But while this is one possible reading of the sentence, 'one of us may jump' also has a reading on which it states that it is permissible that one of us jumps. There is a kind of de re/de dicto ambiguity here, which suggests that 'may' can not only apply to properties but also to propositions.
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