Plausibility is much on the collective mind of the legal profession these days. The Supreme Court set the stage in *Twombly* and *Iqbal*, resetting federal civil pleading to a “plausibility standard.” Now, judges, practicing lawyers, and commentators have been struggling to predict the extent of change wrought by these cases and how far outside of their factual contexts they may apply.
Rarely addressed in the literature is the impact of Iqbal on diversity cases. Federal courts sitting in diversity, of course, always face *Erie* choice-of-law questions, as they are tasked with minimizing forum shopping by distinguishing procedural matters in which federal rules govern from substantive issues that must be controlled by state law. While the pleading standard may seem to be the prototypical procedural rule, state laws that adopt heightened pleading standards to serve substantive ends cast doubt upon this presumption.
State affidavit-of-merit laws are illustrative. These requirements serve the substantive end of effecting MedMal reform by requiring an affidavit of merit to be filed with, or soon after, the complaint. The method used, however, is procedural: these laws implicate the pleading standard for MedMal cases.
Even before *Twombly* and *Iqbal*, the task of characterizing a state substantive policy effected through a procedural mechanism presented a conundrum for diversity courts. But which rule should win out under the now-heightened federal pleading standard? With an eye to both the system and the policy underlying *Erie*, does federal or state law prevail?