Full Idea
For each particular it is likely that there exists at least one individuating conjunction of properties, that is, a conjunction of properties such that the particular instantiates this conjunction and nothing else does.
Gist of Idea
It is likely that particulars can be individuated by unique conjunctions of properties
Source
David M. Armstrong (What is a Law of Nature? [1983], 02.3)
Book Reference
Armstrong,D.M.: 'What is a Law of Nature?' [CUP 1985], p.14
A Reaction
Armstrong commits to a famous Leibniz view, but I don't see his grounds for it. There is nothing incoherent about nature churning out perfect replicas of things, such as quarks and electrons. Would we care if two pens were perfectly identical?