The question is about identity while identity theory already
exist. Say for someone who does not know that Vienna is
the same city as Wien (German) , Wenen (Dutch), Bec (Serbo-
Croatian), etc. We are used to think that names have unique
reference. But there are different names with the same reference.
This made ''logical conclusion'' about the truth possible :
''whatever is true about Vienna is also true about Wien, Wenen
and Bec (grin). This is called ''substitutio salva veritate'' . One
can substitute any of those names for each other and retain
the truth.