What is the role of the antecedent clause in a conditional? Examining a set of conditional expressions that restrict the tense/aspect of the antecedent clause, this work argues that these all arise from a single modal restriction: some conditional devices require the antecedent to be open in a historical modal base. This suggests that conditionals can invoke modality in the antecedent that is independent of the modal flavor of the consequent, that this is a linguistically-relevant dimension of contrast in conditionals, and therefore that some part of conditional `iffiness’ must be lexically specified. This is difficult to explain under analyses where the antecedent simply restricts the domain of evaluation of the consequent.