Wednesday, June 06, 2012

logical sufficiency vs. ontological priority.

Suppose it’s true that
(1)  Sam is the tallest person in the world.
It follows from the truth of (1) (“and” Leibniz’ law) that
(2) Sam is not identical to any thing else,
for (1) predicates of Sam a property that no other thing has. We might be tempted to think that because (2) follows logically from (1) that (1) is what makes Sam self-identical. But this is a mistake, and for two reasons.
The first (and principal) reason is because of the seemingly obvious fact that Sam’s self-identity is more basic than his being the tallest person in the world.  Surely Sam’s being the individual he is is prior to and more basic than his being the tallest man in the world.  It is because Sam is an individual first that it’s possible that he be the tallest man in the world, and not vice-versa.
The second (and less principal) reason (that might just be a consequence of the first reason) why (1) isn’t what grounds the truth of (2) is the seemingly uncontroversial fact that Sam would still be Sam if (it were true) that he is not the tallest man in the world.  And if it’s true that Sam would be Sam if he weren’t the tallest man in the world, whatever makes Sam the individual that he is is prior to and more basic than the fact that he is fact the tallest man in the world.
What follows from this seem to be three related points:
(A) Though a logical consequence of statement might be a thing’s self-identity, this fact alone does not mean that the content of that true statement is what makes that thing self-identical.
(Why not, you ask? Because:)
(B) The logical relationship between statements (e.g. (1) and (2)) presuppose the self-identity of things.  That’s why statements can entail other statements about a thing’s being self-identical.  But given that logic simply presupposes identity, the investigation of what makes a thing self-identical is an ontological question (viz.— it’s a question about the necessary structure of reality).
(C)  Merely unique properties are not sufficient to ground a thing’s self-identity.  Therefore, the ontological investigation as to what does ground a thing’s identity will be incomplete if it ends there. 


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