more from David Wiggins

Single Idea 16521

[catalogued under 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


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

Book Reference

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.