Even though explanation plays a central role in science, it is not enough to simply come up with explanations. Scientists (and everyone else) must also evaluate explanations. After all, it’s clear that not every explanation is a good one, as well as that some explanations are better than others. For example, evolutionary theory provides a much better explanation of the diversity of life than, say, the hypothesis that all organisms appeared at the same time in their present form. But what makes one explanation better than another? Relatedly, how can we tell which of a set of competing hypotheses provides the best explanation?