A necessary part of David Armstrong's account of truthmakers for modal truths is his Possibility principle: any truthmaker for a contingent truth is also a truthmaker for the possibility of the complement of that contingent truth (if T makes _p_ true and _p_ is contingent, then T makes ⋄∼_p_ true). I criticize Armstrong's Possibility principle for two reasons. First, his argument for the Possibility principle both relies on an unwarranted generalization and vitiates his desire for relevant truthmakers. His argument undercuts (...) relevant truthmakers by entailing that each contingent being is a truthmaker for all modal truths. Second, even if the argument seems successful, the Possibility principle is subject to counterexamples. Armstrong's being composed of more than fifty atoms makes it true _that something composed of more than fifty atoms exists_ and that truth is contingent, but his being composed of more than fifty atoms does not make it true _that it is possible that it is not the case that something composed of more than fifty atoms exists_. (shrink)