Re-Evaluating the Role of Simplicity in Explanation Evaluations

People often prefer simpler explanations (i.e., those which invoke fewer unexplained causes), even when such preferences exceed what is justified by the relevant probabilities. This has been taken as evidence that simplicity plays a distinct psychological role in explanatory judgment. However, it remains unclear whether these simplicity biases reflect a genuine role for simplicity or are better explained by other factors. The current studies thus investigated the source of biases towards simpler explanations, as found in previous work. Results showed that, contrary to previous suggestions, simplicity biases did not arise in estimates of explanations’ prior probabilities (instead, priors showed complexity biases due to mathematical errors). Moreover, while simplicity biases sometimes arose directly in estimates of posterior probabilities, these biases disappeared when the complex explanation was described in a more cognitively accessible way, or after repeated exposure to similar scenarios—despite no change in the number of causes in the explanations. These findings suggest that the observed biases are not driven by simplicity as typically defined in this work (in terms of the number of causes), but may instead reflect a preference for explanations that are cognitively simpler, in terms of being easier to process. This work challenges dominant interpretations of simplicity biases, and highlights the importance of distinguishing more cognitive vs. structural forms of simplicity. More broadly, it underscores the importance of ruling out alternative explanations for biased explanation preferences, and offers new directions for understanding the role of simplicity and other explanatory virtues in people’s everyday explanatory reasoning.