Full Idea
If two worlds differ in what they represent de re concerning some individual, but do not differ qualitatively in any way, I shall call that a haecceitist difference. Haecceitism, then, says there are at least some haecceitist differences between worlds.
Gist of Idea
Haecceitism implies de re differences but qualitative identity
Source
David Lewis (On the Plurality of Worlds [1986], 4.4)
Book Reference
Lewis,David: 'On the Plurality of Worlds' [Blackwell 2001], p.221
A Reaction
Lewis bases this view on Kaplan. My brief summary of this is that 'identity may be hidden'. If all electrons are different, what distinguishes them?