 Davidson uses the interaction principle to establish directly one part of mental anomalism—psychological anomalism, which denies the possibility of strict, purely psychological laws of the form ‘M1 &amp; M2 → M3’ (Davidson 1970, 224; 1974b, 243). For if physical events causally impact on mental events, then the mental domain is ‘open’, and any laws in which mental predicates figure will have to take this into account (for related discussion, see the supplement on  Causal Closure of the Physical in the Argument for Anomalous Monism).  More generally, physical conditions will always play some role in any plausible psychological generalizations, because physical intervention (e.g., injury) is always a possibility and can prevent the occurrence of the consequent ‘M3’. Thus, the only potentially true and strict laws in which psychological predicates can figure are variants of the psychophysical form ‘P1 &amp; M1 &amp; M2 → M3’. Psychophysical anomalism, the other component of mental anomalism and the one that denies the possibility of such strict laws, is thus the view that Davidson focuses on establishing.