 However, if identity is a relation, then, given serious actualism, one is not self-identical at worlds in which one fails to exist. This might suggest restricting necessitation to theorems provable without any instance of Id1, which would block not only the inference from line 3 to line 4 but also the  proof of the more general necessitist principle  \(\Box\textbf{N}\) that, necessarily, everything necessarily exists, \(\Box\forall \sfx \Box\exists \sfy\, \sfy=\sfx\). However, that would still not be enough for, as we saw above, necessitism also follows immediately from the instance  CBF*  of the converse Barcan formula, whose  proof  involves no instance of Id1.