 For bottom-up theorists, delusions involve modifications of the belief system that are caused by ‘strange experiences’ due to organic malfunction (Bayne and Pacherie 2004a; Davies et al. 2001). For instance, I experience people watching me with suspicion or hostility, and as a result I form the hypothesis that they intend to cause me harm; or something does not feel right when I see my sister’s face, and as a result I come to believe that the person I am looking at is not really my sister but an impostor.