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Single Idea 14065

[filed under theme 9. Objects / F. Identity among Objects / 8. Leibniz's Law ]

Full Idea

For two things to be strictly identical, they must have all properties in common. That means, among other things, that they must start to exist at the same time and cease to exist at the same time.

Gist of Idea

Two identical things must share properties - including creation and destruction times

Source

Allan Gibbard (Contingent Identity [1975], I)

Book Ref

-: 'Journal of Symbolic Logic' [-], p.188

A Reaction

I don't accept that coming into existence at time t is a 'property' of a thing. Coincident objects give you the notion of 'existing as' something, which complicates the whole story.

The 18 ideas with the same theme [identical objects must have identical features or truths]:

11840 Only if two things are identical do they have the same attributes [Aristotle]
16768 Two things are different if something is true of one and not of the other [Duns Scotus]
17255 Two bodies differ when (at some time) you can say something of one you can't say of the other [Hobbes]
17173 Two substances can't be the same if they have different attributes [Spinoza]
16073 Leibniz's Law is incomplete, since it includes a non-relativized identity predicate [Geach, by Wasserman]
4942 The indiscernibility of identicals is as self-evident as the law of contradiction [Kripke]
11839 Do both 'same f as' and '=' support Leibniz's Law? [Wiggins]
11845 Substitutivity, and hence most reasoning, needs Leibniz's Law [Wiggins]
14065 Two identical things must share properties - including creation and destruction times [Gibbard]
14074 Leibniz's Law isn't just about substitutivity, because it must involve properties and relations [Gibbard]
16019 Leibniz's Law must be kept separate from the substitutivity principle [Noonan]
16018 Indiscernibility is basic to our understanding of identity and distinctness [Noonan]
6049 Leibniz's Law says 'x = y iff for all P, Px iff Py' [McGinn]
6050 Leibniz's Law presupposes the notion of property identity [McGinn]
6048 Leibniz's Law is so fundamental that it almost defines the concept of identity [McGinn]
12236 Leibniz's Law is an essentialist truth [Oderberg]
14754 If you say Leibniz's Law doesn't apply to 'timebound' properties, you are no longer discussing identity [Sider]
16225 If two things might be identical, there can't be something true of one and false of the other [Hawley]