Full Idea
A relation of negation might hold between two beliefs without there being anything that determines which belief is the negative one.
Gist of Idea
If one proposition negates the other, which is the negative one?
Source
Gilbert Harman ((Nonsolipsistic) Conceptual Role Semantics [1987], 12.1.4)
Book Reference
Harman,Gilbert: 'Reasoning Meaning and Mind' [OUP 1999], p.210
A Reaction
[He attributes this thought to Brian Loar] This seems to give us a reason why we need a semantics for a logic, and not just a structure of inferences and proofs.