In the latest issue of PNAS, there's an article on blindsight in ordinary people: The researchers induced local and temporary blindness by magnetically de-activating certain parts of brain area V1. When forced to choose, the subjects then often guessed correctly the direction or colour of a patch which they didn't consciously see.
(As usual, "consciously" is here functionally defined: what the subjects were missing is not some kind of non-functional, phenomenal consciousness, but a state with a certain functional role, leading in particular to utterances like "I saw a yellow patch". A case of truly phenomenal blindsight would be somebody who behaves in every way as if she consciously sees the patches, but who nevertheless doesn't see them consciously.)
What does it take for something to be a perfectly reliable indicator
of something else?
I'm not really familiar with discussions of reliability in epistemology, and I'd be grateful for pointers. Anyway, here is my own suggestion.
First, we need a mapping from (possible) states of the indicator to
the indicated facts (or states or propositions).
Let's say that the indicator displays that p, for short: I(p), if its state is mapped to p by that mapping. The mapping may
be any old function (but the 'states' may not be any old Cambridge
states): there is a good sense in which a clock that consistently runs 8 minutes fast is reliable; the tricky bit is only to read what it says, to figure out
the mapping. This is the sense of "reliable" I'm interested in.
Sunrise from my office window. Til September 2006, I now work as a lecturer in philosophy at the
University of Bielefeld.
I've moved around some things here on the blog. This ought to show up as a smaller note. Let's see.
I thought after finishing my PhD thesis I would spend less time thinking and writing about Lewis for a change. But just then, Brian started his Lewis blog raising all kinds of interesting issues, like how to handle theoretical terms in multiply realised theories. I think Lewis's early suggestion to treat the terms as empty in those cases is much worse than he realised (than he realised even later, when he dropped the suggestion). I hope to say more about that later.
What would you say if it turns out that the watery stuff in our rivers and lakes doesn't actually consist of H2O, but of XYZ: would you say that water consists of H2O or XYZ?
What would you say if it turns out that you are Leverrier's wife living in 1845 and the heavenly body your husband calls "Neptune" is not a planet, but a spaceship: would you say that Neptune is a spaceship or a planet?
There's something odd about the second question.
I am disposed to assent to certain sentences under certain conditions, to "it's raining" if it's raining, etc. For each sentence, this determines a function from conditions -- sets of centered worlds -- to truth values. (If I am disposed to assent to S under condition C, that doesn't mean I assent to S in all C-worlds. I need only do so in the closest C-worlds. I am not disposed to assent to "it's raining" under the condition that it's raining and I am halluzinating that it doesn't rain.)
Sometimes, a counterfactual is true even though the consequent is false in the closest world where the antecedent is true:
1) If Hurricane Katrina hadn't hit the town with 200 km/h, completely destroying our house, we would be at home now, watching TV.
Presumably, at the closest worlds where Hurricane Katrina doesn't hit the town with 200 km/h and completely destroys the house, it hits the town a little faster or slower, still completely destroying the house. Even at the closest worlds where the hurricane doesn't completely destroy the house, it destroys it almost completely, still preventing the TV event.
About half a minute ago, I've poured tea into this cup. In a few seconds, I will take a
sip. What if I had taken a sip a minute earlier? I wouldn't have taken
a sip of tea from an empty cup: that is impossible. So there would
have been tea in the cup a minute ago. How did it get there? Maybe
I would have poured it in earlier. Or maybe it would have tunnelled
directly from the pot into the cup. Or maybe the tea would have
just materialized out of thin air. Some of these counterfactuals
do not sound very plausible, but let's assume that for the kind of
counterfactuals relevant to causation, they are all equally good so
that there is no fact of the matter about how the tea got into the cup
at the closest world where I take the sip a minute earlier: it does
so differently at different worlds that are equally close. (See Lewis,
"Counterfactual Dependence and Time's Arrow" for the standards of
evaluating such counterfactuals, and "Are we free to break the
laws?" for the indeterminacy of divergence miracles.)
Argument 1:
- Hesperus is identical to Phosophorus.
- By modal logic,
.
- Therefore, Hesperus is necessarily identical to
Phosphorus.
Argument 2:
- Sometimes, one is obliged to do things that are not allowed.
- By deontic logic,
.
- Therefore, sometimes one is obliged to things that are both allowed and not allowed.
Argument 3:
- Necessarily, if the moon essentially consists of green
cheese, then it actually consists of green cheese.
- By provability logic,
.
- Therefore, the moon essentially consists of green cheese.
Argument 4:
- It is now 20 seconds past 19:00 hours.
- It is now 30 seconds past 19:00 hours.
- If it is now 30 seconds past 19:00 hours, it is not now 20 seconds past
19:00 hours.
- By propositional logic,
.
- Therefore, the moon is made of green cheese.
What's wrong with these arguments? They are invalid: their premises
are true, their conclusion false. In each case, the fallacy is to
assume that a principle valid in some formal system is also
valid when translated into English.
Roughly, the principle of recombination says that anything can coexist and
fail to coexist with anything else. But that's too strong: things do
have essential extrinsic properties; if Kripke's origin is essential
to Kripke, Kripke cannot fail to coexist with his ancestors. However, a
perfect intrinsic duplicate of Kripke could fail to coexist with Kripke's ancestors.
So less roughly, the principle of recombination goes somehow like this:
For any things in any possible world there is a world
which contains any number of perfect intrinsic duplicates of all those
things and nothing else (i.e. nothing distinct from all these
duplicates).
What is a perfect intrinsic duplicate? Something that has exactly
the same intrinsic properties as the original. What
is an intrinsic property? A property that belongs to objects
independently of what exists and goes on around them. The
instantiation of an intrinsic property in some region of a world is
independent of the instantiation of intrinsic properties in other
regions.