Every physical theory is defined less by what it permits than by what it makes impossible. This programme compares them by their prohibitions.
A theory is best identified by the thing it cannot do.
Classical correlations cannot exceed a certain strength. Quantum mechanics exceeds it — but stops at a ceiling of its own, and not one step beyond. A third limit sits above both, permitted by causality alone and reached by nothing physical yet known.
The gaps between those three limits are the only place where the candidate theories become distinguishable by experiment. Everything else they agree on.
A bound you failed to beat is not a bound.
A limit is established by proof or it is not established. The difference matters: a search that finds no counterexample constrains the search, not the theory — and most claimed impossibilities in this area are the former wearing the language of the latter.
Each modality is rebuilt from first principles rather than assembled from libraries, so that every prohibition can be traced back to the assumption that produced it. A prohibition inherited from someone else’s implementation is not a prohibition you can defend.
“The ceiling is proved, not searched for.”
