X-Message-Number: 20967
Date: Sat, 25 Jan 2003 15:40:56 -0700
From: Mike Perry <>
Subject: Identity, Equivalence, and "Sameness"

Thomas Donaldson writes

>You prefer (or seem to prefer) the use of "equivalence" rather than
>"identity". What is your reason for this preference?

Mainly, I think it is less confrontational and more acceptable to different 
people with different, fiercely held opinions about "identity." On the 
other hand, it is interesting that not even equivalence is adequate to 
cover all important usages of "identity" as I see it, a point discussed in 
my book (see pp. 242-44). The idea that we are the "same" as some past 
individual, in the sense of being a more developed version or a continuer, 
invokes an entirely different notion of "sameness" or "identity"--A is the 
same entity as B iff either A is a continuer of B or vice versa. (It will 
be seen that this is a kind of ancestor-descendant relationship.) I allow 
reflexivity, that is, A is regarded as a continuer of A, so that A is the 
same as A. Symmetry (if A is the same as B then B is the same as A) follows 
from the definition. But transitivity breaks down: it could happen that 
both B and C are continuers of A but B is not a continuer of C nor is C a 
continuer of B. So we get only two of the three properties of equivalence, 
but still I think this notion of "sameness" is vital, as is argued. (And I 
realize that, to make the notion workable, other issues must be confronted, 
such as the problem of loss of information, when you may not, due to 
forgetting or trauma, be a true continuer of a past version of you--these 
issues are treated at length.)

Mike Perry

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