Full Idea
That a common 'thisness' may underlie extreme dissimilarity or distinct thisnesses may underlie great resemblance I call 'haecceitism'. (I prefer the pronunciation Hex'-ee-i-tis-m).
Clarification
Latin 'haec' means this.
Gist of Idea
'Haecceitism' is common thisness under dissimilarity, or distinct thisnesses under resemblance
Source
David Kaplan (How to Russell a Frege-Church [1975], IV)
Book Reference
'The Possible and the Actual', ed/tr. Loux,Michael J. [Cornell 1979], p.217
A Reaction
[odd pronunciation, if 'haec' is pronounced haeek] The view seems to be very unpopular (e.g. with Lewis, Bird and Mumford). But there is an intuitive sense of whether or not two things are identical when they seem dissimilar.