Full Idea
A uniquely realised theory is, other things being equal, certainly more satisfactory than a multiply realised theory. We should insist on unique realisation as a standard of correctness unless it is a standard too high to be met.
Gist of Idea
It is better to have one realisation of a theory than many - but it may not always be possible
Source
David Lewis (How to Define Theoretical Terms [1970], III)
Book Reference
Lewis,David: 'Philosophical Papers Vol.1' [OUP 1983], p.83
A Reaction
The point is that rewriting a theory as Ramsey sentences just says there is at least one realisation, and so it doesn't meet the highest standards for scientific theories. The influence of set-theoretic model theory is obvious in this approach.
Related Idea
Idea 15528 A Ramsey sentence just asserts that a theory can be realised, without saying by what [Lewis]