What is the role of the antecedent clause in a conditional? Examining a set of restrictions on the tense/aspect of the antecedent clause in Bangla conditionals, I argue that these reflect a single modal restriction: the antecedent proposition must 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.