It has received little attention that the truth values of sequential counterfactuals (i.e. counterfactuals in which the antecedent event precedes the consequent event) can shift over time. In the footsteps of Goodman, I develop a theory of sequential counterfactuals that can account for this feature. The theory (i) defends a semifactual test of cotenability, (ii) spells out the truth conditions for semifactuals in probabilistic terms and (iii) accounts for truth-value shifts by appealing to a dynamic view of time.