 The 1959 paper contains also a proof of the modal counterpart of the Löwenhein-Skolem theorem for first-order logic, according to which if a formula is satisfiable in a non-empty domain then it is satisfiable, and hence valid (true in \(G)\), in a model \((G, K)\) in a domain \(D\), where both \(K\) and \(D\) are either finite or denumerable; and if a formula is valid in every finite or denumerable domain it is valid in every domain.