This study investigates how judgments of explanatory power are affected by (i) the prior credibility of a potential explanation, (ii) the causal framing used to describe the explanation, and (iii) the generalizability of the explanation. We found that the prior credibility of a causal explanation plays a central role in explanatory reasoning: first, because of the presence of strong main effects on judgments of explanatory power, and second, because of the gate-keeping role prior credibility has for other factors. Highly credible explanations were not susceptible to causal framing effects. Instead, highly credible hypotheses were sensitive to the generalizability of an explanation. While these results yield a more nuanced understanding of the determinants of judgments of explanatory power, they also illuminate the close relationship between prior beliefs and explanatory power and the relationship between abductive and probabilistic reasoning.