Full Idea
'Methodological solipsism' says merely that everyone can conceive of themselves as the only subject. Everyone can construct all referents of their thought and talk out of complexes of their very own experience.
Gist of Idea
Methodological Solipsism assumes all ideas could be derived from one mind
Source
Martin Kusch (Knowledge by Agreement [2002], Ch.19)
Book Reference
Kusch,Martin: 'Knowledge by Agreement' [OUP 2004], p.274
A Reaction
The possibility of this can be denied (e.g. by Putnam 1983, dating back to Wittgenstein). I too would doubt it, though finding a good argument seems a forlorn hope.