Full Idea
Fully fledged realism depends on - indeed, may be identified with - an undiluted application to sentences of the relevant kind of straightforwards two-valued semantics.
Clarification
'Two-valued' semantics just recognises True or False
Gist of Idea
Realism is just the application of two-valued semantics to sentences
Source
Michael Dummett (Frege philosophy of mathematics [1991], Ch.15)
Book Reference
Dummett,Michael: 'Frege: philosophy of mathematics' [Duckworth 1991], p.198
A Reaction
This is the sort of account you get from a whole-heartedly linguistic philosopher. Personally I would say that Dummett has got it precisely the wrong way round: I adopt a two-valued semantics because my metaphysics is realist.