Full Idea
Externalists are typically committed to counting expressions as 'synonymous' if they happen to be linked in the right way to the same external phenomena, even if a thinker couldn't realise that they are by reflection alone.
Gist of Idea
Externalist synonymy is there being a correct link to the same external phenomena
Source
Georges Rey (The Analytic/Synthetic Distinction [2013], 4.2)
A Reaction
[He cites Fodor] Externalists always try to link to concrete things in the world, but most of our talk is full of generalities, abstractions and fiction which don't link directly to anything.
Book Reference
'Stanford Online Encyclopaedia of Philosophy', ed/tr. Stanford University [plato.stanford.edu], p.11