Full Idea
A thisness is the property of being identical with a certain particular individual - not the property that we all share, of being identical with some individual, but my property of being identical with me, your property of being identical with you etc.
Gist of Idea
A 'thisness' is a thing's property of being identical with itself (not the possession of self-identity)
Source
Robert Merrihew Adams (Primitive Thisness and Primitive Identity [1979], 1)
Book Reference
'Metaphysics - An Anthology', ed/tr. Sosa,E. /Kim,J. [Blackwell 1999], p.172
A Reaction
These philosophers tell you that a thisness 'is' so-and-so, and don't admit that he (and Plantinga) are putting forward a new theory about haecceities, and one I find implausible. I just don't believe in the property of 'being-identical-to-me'.
Related Idea
Idea 14512 Moderate Haecceitism says transworld identities are primitive, but connected to qualities [Adams,RM]