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Tuesday, October 18, 2011

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Bill,

Sorry I don't get this "the Necessity of Identity" principle. Take this example:
"Obama is the president of the US"
Is this an identity? If so, is this a necessary identity?

Good comment, arash. The principle holds when proper names flank the identity sign. 'The president of the US,' however, is not a proper name but a definite description. When read attributively as opposed to referentially it allows for possible worlds in which Obama is not the present president of the US.

There may be a line of defense for Hennessey here. He wants to read the predication 'Socrates is seated' as the identity sentence, 'Socrates is identical to a seated being.' Now what exactly is the logical status of 'a seated being'? It is not a logically proper name. It is an indefinite description.

Bill,
'Socrates is identical to a seated being' does not sound right. Because if:
1. 'X is seated' means 'X is identical to a seated being'
2. 'Socrates is seated' and 'Obama is seated' are both true
3. Identity is transitive
Then:
4. 'Socrates is identical to a seated being' and 'Obama is identical to a seated being' are both true (for 1 and 2)
5. 'Obama is identical to Socrates' is true (for 4 and 3)

Hennessey would probably say that 'a seated being' means 'some seated being or other' in which case the inference to (5) fails.

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