A common intuition, often captured in fiction, is that some impossible events (e.g., levitating a stone) are “more impossible” than others (e.g., levitating a feather). We investigated the source of this intuition, hypothesizing that it arises from explanatory considerations logically precluded by the violation at hand but still taken into account. In Study 1, adults saw pairs of magical events (spells) that violated one of 18 causal principles and were asked to indicate which would be more difficult to learn. Both spells violated the same causal principle but differed in their relation to a subsidiary principle. Participants’ judgments of spell difficulty consistently honored the subsidiary principle. Study 2 replicated the effects of Study 1 with Likert-type ratings, and Study 3 replicated those effects in children. These findings suggest that events that defy causal explanation are interpreted in terms of explanatory considerations that hold in the absence of such violations.