Full Idea
Objects we find in the actual world might have been so different than they actually are that it appears impossible to identify the same objects from world to world. Kripke sidesteps the problem by saying transworld identity is a decision, not a discovery.
Gist of Idea
Kripke avoids difficulties of transworld identity by saying it is a decision, not a discovery
Source
report of Saul A. Kripke (Naming and Necessity lectures [1970]) by Dale Jacquette - Ontology Ch.2
Book Reference
Jacquette,Dale: 'Ontology' [Acumen 2002], p.77
A Reaction
This is the strategy that opposes Lewis's proposal of 'counterpart' objects that have properties in common. It is also the source of Kripke's causal theory of reference, and hence a key to massive modern debates.