Research has shown that the judged probability of an event depends on the specificity with which the focal and alternative hypotheses are described. In particular, unpacking the components of the focal hypothesis generally increases the judged probability of the focal hypothesis, while unpacking the components of the alternative hypothesis decreases the judged probability of the focal hypothesis. As a consequence, the judged probability of the union of disjoint events is generally less than the sum of their judged probabilities. This article shows that the total judged probability of a set of mutually exclusive and exhaustive hypotheses increases with the degree to which the evidence is compatible with these hypotheses. This phenomenon, which we refer to as the enhancement effect, is consistent with a descriptive account of subjective probability called support theory. © 1997 John Wiley & Sons, Ltd.