Full Idea
Plantinga proposes surrogates for nonexistent things - individual essences that are themselves necessary existents and that correspond one-to-one with all the 'things' that might exist.
Gist of Idea
Plantinga proposes necessary existent essences as surrogates for the nonexistent things
Source
report of Alvin Plantinga (World and Essence [1970]) by Robert C. Stalnaker - Mere Possibilities 1
Book Reference
Stalnaker,Robert C.: 'Mere Possibilities' [Princeton 2012], p.2
A Reaction
There are an awful lot of competing concepts of essence flying around these days. This one seems to require some abstract 'third realm' (or worse) in which these essences can exist, awaiting the arrival of thinkers. Not for me.