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Single Idea 6048

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

Full Idea

Leibniz's Law, which a defender of relative identity might opt to reject, is so fundamental to the notion of identity that rejecting it amounts to changing the subject.

Clarification

The Law says two truly identical things must have the same properties

Gist of Idea

Leibniz's Law is so fundamental that it almost defines the concept of identity

Source

Colin McGinn (Logical Properties [2000], Ch.1 n8)

Book Ref

McGinn,Colin: 'Logical Properties' [OUP 2003], p.5

A Reaction

The Law here is the 'indiscernibility of identicals'. I agree with McGinn, and anyone who loses their grip on this notion of identity strikes me as losing all grip on reality, and threatening their own sanity (well, call it their 'philosophical sanity').

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]
6050 Leibniz's Law presupposes the notion of property identity [McGinn]
6049 Leibniz's Law says 'x = y iff for all P, Px iff Py' [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]