[extropy-chat] Identity (was: Survival tangent)

[Jef Allbright]

Ian -

Unfortunately, this discussion became fragmented, with the result that
it might appear that I was arguing a point of view, when actually I was
arguing only for the use of valid logic.

I don't in fact believe that a person is fully and effectively defined
by their values, beliefs and memories. I think that a more general and
useful definition rests on the concept of shared agency, regardless of
physical form and function.

As to your point about the rigorous meaning of identity, I fully agree.
That being said, within the topic of "personal identity" we are
specifically allowing for the case when two objects, recognized as
persons, appear to be *effectively* the same within a given context.

- Jef

 

-----Original Message-----
From: extropy-chat-bounces at lists.extropy.org
[mailto:extropy-chat-bounces at lists.extropy.org] On Behalf Of Ian Goddard
Sent: Wednesday, November 01, 2006 10:28 PM
To: extropy-chat at lists.extropy.org
Subject: [extropy-chat] Identity (was: Survival tangent)

Jef Allbright wrote:

> Where is it logically shown that all persons must have unique 
> identity?


 The classical definition of 'identity' in logic is found in the
second-order statement quantifying over objects (x, y) and properties of
objects (P):

  AxAy[(x = y) <-> AP(Px <-> Py)]

Literally: for all objects x and y, x is y if and only if for all
properties P, P is a property of x if and only if P is a property of y.
More simply: x is y just in case every property of x is a property of y
and vice versa. 

 Now, given the logical definition of 'identity', if there is a perfect
copy of my brain with all its encoded contents and possible states, that
copy still lacks at least: (1) the property of being 'the original', (2)
the property of being in the location that the original is, and (3) the
property of being encoded on the physical substrate that the original is
encoded on. Ergo, there exists at least one property that the original
has but the copy lacks, and thus, by the definition of 'identity', any
claim that "the original = the copy" is false. QED



> Slawomir, A and B are symbols representing antecedent and consequent 
> in the form of a syllogism.  The particulars don't matter if the form 
> is logically invalid.
> In this particular case, A->B corresponds to the statement "any person

> is defined by values, beliefs and memories".  This does not imply the 
> statement
> B->A corresponding to "any values, beliefs and
> memories define a person" because not all values, beliefs and memories

> are associated with any given person.  It's not symmetrical.


 By denoting 'Any person', your statement "Any person is defined by
values, beliefs and memories"
*quantifies* over the set of all people. So the proposed formula of
propositional logic 'A->B' is not an indicated model. The statement
instead points to a quantified model in predicate logic, something more
like: "For all x, if x is a person, then x is defined by values, beliefs
and memories." 

 Consider also, in that statement you quantify over the set of all
people, but in your interpretation of its converse 'B->A' you quantify
over the set of all values, beliefs, and memories, saying: "Any values,
beliefs and memories define a person." Apart from my previous
observation about 'identity', I'm not taking a side in all aspects of
the discussion, but it might be helpful to explicitly articulate the
analytic model you're proposing. ~Ian


http://IanGoddard.net

"A proposition can be true or false only in virtue of being a picture of
reality." - Wittgenstein


 



 
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