 Thus, according to Adams, de re modal propositions are existence entailing: an (actually existing) modal proposition \(\Box\varphi\) or \(\Diamond\varphi\) can be true at a world only if it exists there and, hence, only if its subjects do as well. This idea can be axiomatized by a modalized version of the serious actualism principle GSA (see Adams’ principles (C6) and  (C7)[90]):