 When Davidson first argued for Anomalous Monism he subscribed to a causal criterion of event-individuation, according to which two events (event-descriptions) are identical (co-refer) if they share all the same causes and effects (Davidson 1969). He much later came to reject that criterion in favor of one according to which events are identical if and only if they occupy the same spatiotemporal region (Davidson 1985b). The difference between these views will not, however, be reflected in our discussion. It does not appear to affect either the derivation or the essential nature of Anomalous Monism. For our purposes, Davidson’s central claims are that what makes an event mental (or physical) is that it has a mental (or physical) description, and the extensionalist thesis that events are concrete entities that can be described in many different ways (‘the flipping of the light switch’, ‘the illuminating of the room’ and ‘the alerting of the burglar that someone is home’ can all pick out the same one event in different terms). (For controversies concerning extensionalism, see  5.2  and the supplement on  Related Issues  (Anomalous Monism and Scheme-Content Dualism).)