step to recognizing metaphysically

step to recognizing metaphysically impossible, but epistemically
possible, members of W. These are maximal world-representing
properties that couldn’t have been instantiated (because they deny
that an object has one of its essential properties), but which cannot
be known apriori not to be instantiated (Soames 2005a, 2006,
2007a). For example, since nonidentity necessarily relates any pair
it actually relates, even though empirical knowledge is needed to
determine which pairs these are, world-states in which I am Saul
Kripke are epistemically, but not metaphysically, possible.
A related point, involving the essentiality of origin, is made
in Salmon (1989). The key example involves a ship s originally
constructed from certain material. It is, Salmon plausibly maintains,
a necessary truth that if s originated from material m, then
s could have originated from material slightly different from m,
even though S couldn’t have originated from material too different
from m (where “too different” is spelled out). Given this, we
can construct a series of world-states—beginning with the actual
state @ in which S originated from boards b1 . . . bn. Each succeeding
world-state wi+1 substitutes a new board for one of those from
which S originated in wi. Although each state is possible from
the preceding one, we are bound to reach world-states that are
impossible from @. Thus, relative possibility isn’t transitive, and
both S4 and S5 fail. Given Salmon’s statement of the metaphysical
facts, the argument shows that (