Full Idea
If Fido's being possibly black reduces (in Lewis's account) to the existence of black counterparts of Fido, then 'Fido is possibly black' is actually true, but it has no actually existing truthmaker.
Gist of Idea
If 'Fido is possibly black' depends on Fido's counterparts, then it has no actual truthmaker
Source
Trenton Merricks (Truth and Ontology [2007], 5.I)
Book Reference
Merricks,Trenton: 'Truth and Ontology' [OUP 2007], p.99
A Reaction
This problem is increasingly the target of my views about dispositions and powers. Fido is not possibly a prize-winning novelist, but is possibly dead or in good health, because of the actual nature and dispositions of Fido.