Re: counterparts

[Keith Wilson <kw503@york.ac.uk>]

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Hi James,

The best thing I've read on possible worlds and counterparts is Saul 
Kripke's Naming and Necessity, which I'd highly recommend (especially 
Lecture I, pp. 41-53 and 57-62). He critiques the whole idea of 'transworld 
identification' and Lewisian counterparts as being like trying to identify 
other possible worlds 'as if through a telescope', i.e. by their 
qualitative properties. Kripke says -- quite rightly, I think -- that 
identity across possible worlds is not 'seen from a distance' in this way, 
but stipulated in advance, and so whether the things or people in them are 
the same as (i.e. numerically identical with) the ones in this world is 
determined by the way that you set up the particular possible world in your 
description.

For example, a possible world in which I am a small green frog does contain 
me, because I have specified in advance that I am in it (albeit in the form 
of a small green frog). Similarly, a possible world in which I was a female 
member of the same family and had a brother called Keith who studies 
philosophy at the University of York would contain me (as the sister) and 
someone who was not me, even though they may have all of my current 
qualitative properties (this contradicts the Lewisian account in which my 
counterpart would be the latter individual). I don't think it would be 
possible for me to be my own sister in any possible world that has same 
biology as this one, as this would require me to be two individuals at the 
same time. (I'm not sure how Kripke would account for the statement that I 
could have been twins, for example, but here it is unclear whether these 
twins would also have been me, so maybe this is a special case.)

On Kripke's view, names are 'rigid designators' that refer to the same 
object in all possible worlds where that object exists. So in your example 
of the twins, James 1 would be a devilishly handsome philosophy student and 
James 2 a swashbuckling pirate, just as you've stipulated when setting up 
the possible worlds.

Kripke's views on essential properties are a little more tricky, and I'm 
not sure I understand them fully. At one point he says that a thing's 
essential properties depend upon the way it is described, but then later on 
he says that there are genuine essential and non-essential properties that 
are independent of descriptions. I can't quite remember the example he 
gives and haven't read Lecture III yet, so you might want to check up on 
this one, or perhaps someone else can fill in the details.

Hope this helps!

- Keith



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