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Single Idea 16521

[filed under theme 9. Objects / F. Identity among Objects / 6. Identity between Objects ]

Full Idea

The famous proof of Barcan Marcus about necessity of identity comes down to simply this: Hesperus is necessarily Hesperus, so if Phosphorus is Hesperus, Phosphorus is necessarily Hesperus.

Gist of Idea

A is necessarily A, so if B is A, then B is also necessarily A

Source

David Wiggins (Sameness and Substance [1980], 4.3)

Book Ref

Wiggins,David: 'Sameness and Substance' [Blackwell 1980], p.110

A Reaction

Since the identity of Hesperus and Phosphorus was an a posteriori discovery, this was taken to be the inception of the idea that there are a posteriori necessities. The conclusion seems obvious. One thing is necessarily one thing.

The 20 ideas with the same theme [two objects turning out to be one object]:

15847 Two things relate either as same or different, or part of a whole, or the whole of the part [Plato]
15825 Carneades denied the transitivity of identity [Carneades, by Chisholm]
9853 Identity between objects is not a consequence of identity, but part of what 'identity' means [Frege, by Dummett]
18440 Identity of physical objects is just being coextensive [Quine]
17038 If Hesperus and Phosophorus are the same, they can't possibly be different [Kripke]
17036 Identity statements can be contingent if they rely on descriptions [Kripke]
9905 Identity statements make sense only if there are possible individuating conditions [Benacerraf]
16224 There can't be vague identity; a and b must differ, since a, unlike b, is only vaguely the same as b [Evans, by PG]
16521 A is necessarily A, so if B is A, then B is also necessarily A [Wiggins]
14073 Claims on contingent identity seem to violate Leibniz's Law [Gibbard]
15969 Two things can never be identical, so there is no problem [Lewis]
6047 All identity is necessary, though identity statements can be contingently true [McGinn]
5494 'Lightning is electric discharge' and 'Phosphorus is Venus' are synthetic a posteriori identities [Lycan]
15074 We would understand identity between objects, even if their existence was impossible [Fine,K]
16027 If two things are equal, each side involves a necessity, so the equality is necessary [Gallois]
16231 Occasional Identity: two objects can be identical at one time, and different at others [Gallois, by Hawley]
14081 Identities can be true despite indeterminate reference, if true under all interpretations [Schaffer,J]
16360 Identity statements are informative if they link separate mental files [Recanati]
14477 Identical entities must be of the same category, and meet the criteria for the category [Thomasson]
14476 Identity claims between objects are only well-formed if the categories are specified [Thomasson]