This article demonstrates that the A/Ā distinction is an epiphenomenon that emerges from independently necessary properties of Merge and the interpretive components. A true explanation of the A/Ā distinction requires that the distinction between the two classes of structures must emerge from a conspiracy of independently motivated principles and that the distinction should explain why the contrasts between A- and Ā-constructions are precisely the ones they are. I argue that certain moved constituents must be structurally altered on the way to their landing sites; otherwise, they will interfere with Case and agreement relations. I propose that an optional instance of Merge, late attachment of a prepositional head to the moved DP, “insulates” that DP from Case and agreement, but has consequences for what an insulated DP can antecede and/or license. Insulation is optional, but limited by independently motivated interface requirements that determine its distribution. The distribution of insulation explains why A- and Ā-structures differ in just the ways they do and not in other ways.