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Beliefs about bad people are volatile


People form moral impressions rapidly, effortlessly and from a remarkably young age1,2,3,4,5. Putatively ‘bad’ agents command more attention and are identified more quickly and accurately than benign or friendly agents5,6,7,8,9,10,11,12. Such vigilance is adaptive, but can also be costly in environments where people sometimes make mistakes, because incorrectly attributing bad character to good people damages existing relationships and discourages forming new relationships13,14,15,16. The ability to accurately infer the moral character of others is critical for healthy social functioning, but the computational processes that support this ability are not well understood. Here, we show that moral inference is explained by an asymmetric Bayesian updating mechanism in which beliefs about the morality of bad agents are more uncertain (and therefore more volatile) than beliefs about the morality of good agents. This asymmetry seems to be a property of learning about immoral agents in general, as we also find greater uncertainty for beliefs about the non-moral traits of bad agents. Our model and data reveal a cognitive mechanism that permits flexible updating of beliefs about potentially threatening others, a mechanism that could facilitate forgiveness when initial bad impressions turn out to be inaccurate. Our findings suggest that negative moral impressions destabilize beliefs about others, promoting cognitive flexibility in the service of cooperative but cautious behaviour.

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Fig. 1: Learning task and model.
Fig. 2: Asymmetry in moral impression formation, study 2.
Fig. 3: Forming impressions of morality versus competence, study 3.
Fig. 4: Inferences about moral character affect learning about non-moral traits and impression updating.

Data availability

The data that support the findings of this study are available from the corresponding author upon request.


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We thank D. Carlston, E. Boorman, C. Summerfield and T. Behrens for helpful feedback. We thank T. Tyurkina and L. Caviola for developing the web applications utilized in studies 2–7 for data collection. J.Z.S. was supported by a Clarendon and Wellcome Trust Society and Ethics award (104980/Z/14/Z). R.B.R. was supported by a MRC Career Development award (MR/N02401X/1). This work was supported by a Wellcome Trust ISSF award (204826/Z/16/Z), the John Fell Fund and the Academy of Medical Sciences (SBF001/1008). The funders had no role in study design, data collection and analysis, decision to publish or preparation of the manuscript.

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Authors and Affiliations



M.J.C. and J.Z.S. conceived the studies. J.Z.S., C.M., R.B.R. and M.J.C. designed the studies. J.Z.S. collected the data. J.Z.S., C.M. and M.J.C. analysed the data. J.Z.S. and M.J.C. wrote the manuscript with edits from R.B.R. and C.M.

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Correspondence to Molly J. Crockett.

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Supplementary information

Supplementary Information

Supplementary Methods, Supplementary Results, Supplementary Tables 2–4, 6–12 and Supplementary Figures 1–7

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Supplementary Table 1

Supplementary Table 5

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Siegel, J.Z., Mathys, C., Rutledge, R.B. et al. Beliefs about bad people are volatile. Nat Hum Behav 2, 750–756 (2018).

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