 One central question is whether our contractualist evaluation of risk should be ex post or ex ante. Contractualism tells us to justify our moral principles to each person. A principle permitting driving must be justified to Bob. But when do we imagine this justification occurring? Suppose we were to offer Bob a choice between two principles: one permits driving and the other forbids it. When does Bob make this choice? Does he choose in advance – perhaps before he moves to the city or before his life begins? Or does he choose in retrospect – after he knows how his life has actually gone?