Persistent bias in expert judgments about free will and moral responsibility: A test of the expertise defense

► Documents bias in expert judgments about free will and moral responsibility. ► Challenges the expertise defense used to insulate philosophers’ reasoning. ► Shows that bias is predicted by a heritable personality trait (i.e., extraversion). ► Introduces a reliable, validated test of expert knowledge in free will debates. ► Implications for the practice of philosophy and professional ethics (law, medicine). Many philosophers appeal to intuitions to support some philosophical views. However, there is reason to be concerned about this practice as scientific evidence has documented systematic bias in philosophically relevant intuitions as a function of seemingly irrelevant features (e.g., personality). One popular defense used to insulate philosophers from these concerns holds that philosophical expertise eliminates the influence of these extraneous factors. Here, we test this assumption. We present data suggesting that verifiable philosophical expertise in the free will debate—as measured by a reliable and validated test of expert knowledge—does not eliminate the influence of one important extraneous feature (i.e., the heritable personality trait extraversion) on judgments concerning freedom and moral responsibility. These results suggest that, in at least some important cases, the expertise defense fails. Implications for the practice of philosophy, experimental philosophy, and applied ethics are discussed.