 TSB  For any possible worlds \(w\) and \(w'\), if \(w\) and \(w'\) agree as regards what things there are, and for any \(n\), any perfectly natural \(n\)-ary property \(R\), and any \(n\) objects \(x_1,\ldots,x_n\) that exist at \(w\) and \(w'\), the proposition that \(R(x_1,\ldots,x_n)\) is true at \(w\) if and only if it is true at \(w'\), then exactly the same propositions are true at \(w\) and  \(w'\).[30] 