Full Idea
To be real in the scientific sense means to be an element of the system; hence this concept cannot be meaningfully applied to the system itself.
Gist of Idea
To be 'real' is to be an element of a system, so we cannot ask reality questions about the system itself
Source
Rudolph Carnap (Empiricism, Semantics and Ontology [1950], 2)
Book Reference
Carnap,Rudolph: 'Meaning and Necessity (2nd ed)' [Chicago 1988], p.207
A Reaction
I'm not sure why there has to be a specifically 'scientific sense' to beig real. It is common sense, though, that the concepts within a system cannot be unthinkingly applied to the system itself. Chess sets don't make knight moves.