 Probabilism imposes synchronic conditions on degrees of belief. But how should subjective probabilities be updated when new information is received? Update rules are diachronic conditions that tell us how to revise our subjective probabilities when we receive new information. There are two standard update rules. Strict conditionalization applies when the new information receives the maximal degree of belief. Jeffrey conditionalization allows for the situation in which no proposition is upgraded to full certainty when new information is acquired. In the first case, probabilism is extended by