Posted by alexandra_k on August 16, 2005, at 18:11:26
In reply to Re: robot brains, posted by alexandra_k on August 16, 2005, at 17:26:52
what on earth is meaning?
what does 'water' mean?
one part of meaning is reference.
what does 'water' mean? well... it means the set of all objects that the term is correctly applied to. all the past samples of water, all the present samples of water, and all the future samples of water as well.On the actual world it turns out that the stuff that we were causally acquainted with, the stuff that we dubbed 'water' just is one and the same thing (roughly) as H2O.
So in one sense, water means H2O. We start with a term that is associated with a sample of stuff by ostensive definition. Ostensive definition: 'that (gesture) is water'. That is a baptism or naming ceremony. Then other speakers use the term with the intention to refer to the same sort of stuff as the person they heard the term off. In that way there is a causal chain that links the term to the stuff.
The scientists study that stuff... And what they discover is its essential nature: turns out that that stuff gets to be the same kind of stuff in virtue of having the same chemical constitution: H2O. So now we can say that H2O means water.
Now... Lets do some space travelling...
(Credit to Hillary Putnam) We discover a planet (over the other side of the sun) that turns out to be EXACTLY qualitatively identical to this world. Everything looks EXACTLY the same. You even have a counter-part on twin earth. Someone that looks and thinks just like you. Has all the experiences you have had etc etc.On this world the scientists have made an interesting discovery. The essential nature of the stuff that the twin earthians have dubbed 'water' actually has chemical composition xyz. Now it turns out that thats not just another way of saying H2O. Rather, the stuff they dubbed water, the stuff that falls from the sky and fills the lakes, the drinkable, potable stuff has a radically different chemical composition to earthian water. Qualitatively is appears exactly the same, but scientifically its essental nature is radically different.
Now... Some questions...
The twin earthians call xyz 'water'. Does the twin earth expression 'water' have the same or different extension (set of samples in the world) that the earthian expression 'water' has?
Do the twin earthian and earthian expressions 'water' mean the same thing?Consensus (fairly much - one shouldn't say that really...) is that the terms have different extensions. They refer to different samples of stuff with different essential natures.
The terms have the same meaning, however. Qualitatively there is no difference between the concepts that the earthians and twin earthians have. Our concepts are the same: they pick out the sample by its superficial properties of 'watery stuff' the clear liquid that fills the lakes etc...
And what this is supposed to show us...
The essential nature of things is to be determined by science (and is thus a-posteriori, it is an empirical matter).
We use terms without knowing the essential nature, but when it comes to learning about the essential nature we defer to the experts...Given that water turned out to be H2O on earth the earthian expression 'water' necessarily refers to H2O.
It could have been true that the earthian expression 'water' referred to xyz only in the sense that given the state of our knowledge a couple hundred years ago it seemed from our point of view to be possible...
But actually, it is not possible that the earthian expression 'water' refers to xyz at all. GIVEN the essential nature of water being what it is it is necessary that the essential nature of water is what it is.
And this is how Kripke shows us that there is such a thing as a-posteriori, empirical, to be determined by science necessity. It isn't just that analytic statements are necessary.
'Water = H2O' is a-posteriori...
But it is necessary as well...
Which is just to say that...
Water = H2O in all possible worlds.And that it is possible...
That there be another world (lets say behind the sun as well) where H2O is black and tarry. Its this black and tarry stuff that paves the roads. On this second twin earth they call this stuff 'tar'. But it turns out that 'tar' (in twin earthian) is coextensive (picks out the same stuff) as 'water' in earthian. And the correct thing to say in earthian english is 'golly gee, you pave your roads with water over here!'
Crazy philosophers, eh???
poster:alexandra_k
thread:541758
URL: http://www.dr-bob.org/babble/write/20050807/msgs/542603.html