 Indiscernibility  \(x\) is qualitatively indiscernible from \(y\) if and only if there is a one-to-one, onto function \(f\) whose domain and range include all objects, such that \(f(x)=y\), and for any sequence \(x_1,\ldots ,x_n\) of objects and any perfectly natural \(n\)-ary property \(R\), \(x_1,\ldots ,x_n\) instantiate \(R\) just in case \(f(x_1),\ldots ,f(x_n)\) instantiate \(R\). 