Full Idea
If two objects have the same logical form, the only distinction between them, apart from their external properties, is that they are different.
Gist of Idea
Two objects may only differ in being different
Source
Ludwig Wittgenstein (Tractatus Logico-Philosophicus [1921], 2.0233)
Book Reference
Wittgenstein,Ludwig: 'Tractatus Logico-Philosophicus (Pears)', ed/tr. Pears,D. /McGuinness,B. [RKP 1961], p.7
A Reaction
This isn't a commitment to haecceities, but it seems to be flirting with the idea. See Simons 1987:241. Kit Fine picks up the idea that objects, as well as sentences, might have 'logical form'. How can being 'different' be primitive? Spatial location?