 Salmon offered a series of counterexamples to Hempel’s approach. In the case of I-S explanations, Hempel required that the nomic expectability of the explanandum must be equal to or greater than .5, which preserved the symmetry thesis for explanations of this kind. This implied that events with low probability could not be explained. There were persuasive illustrations, moreover, demonstrating that explanations could satisfy Hempel’s criteria, yet not explain why their explanandum events occur. For example,