Drawing together social psychologists' concerns with equality and cognitive psychologists' concerns with scientific inference, 6 studies (N = 841) showed how implicit category norms make the generation and test of hypothesis about race highly asymmetric. Having shown that Whiteness is the default race of celebrity actors (Study 1), Study 2 used a variant of Wason's (1960) rule discovery task to demonstrate greater difficulty in discovering rules that require specifying that race is shared by White celebrity actors than by Black celebrity actors. Clues to the Whiteness of White actors from analogous problems had little effect on hypothesis formation or rule discovery (Studies 3 and 4). Rather, across Studies 2 and 4 feedback about negative cases-non-White celebrities-facilitated the discovery that White actors shared a race, whether participants or experimenters generated the negative cases. These category norms were little affected by making White actors' Whiteness more informative (Study 5). Although participants understood that discovering that White actors are White would be harder than discovering that Black actors are Black, they showed limited insight into the information contained in negative cases (Study 6). Category norms render some identities as implicit defaults, making hypothesis formation and generalization about real social groups asymmetric in ways that have implications for scientific reasoning and social equality.