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Full Idea
The necessity of identity: a=b; □(a=a); so something necessarily = a; so something necessarily must equal b; so □(a=b). [A summary of the argument of Marcus and Kripke]
Gist of Idea
If two things are equal, each side involves a necessity, so the equality is necessary
Source
André Gallois (Identity over Time [2011], §3)
Book Ref
'Stanford Online Encyclopaedia of Philosophy', ed/tr. Stanford University [plato.stanford.edu], p.13
A Reaction
[Lowe 1982 offered a response] The conclusion seems reasonable. If two things are mistakenly thought to be different, but turn out to be one thing, that one thing could not possibly be two things. In no world is one thing two things!
| 16025 | If things change they become different - but then no one thing undergoes the change! [Gallois] |
| 16026 | 4D: time is space-like; a thing is its history; past and future are real; or things extend in time [Gallois] |
| 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] |
| 14755 | Gallois is committed to identity with respect to times, and denial of simple identity [Gallois, by Sider] |
| 16233 | Gallois hoped to clarify identity through time, but seems to make talk of it impossible [Hawley on Gallois] |
| 13437 | A CAR and its major PART can become identical, yet seem to have different properties [Gallois] |