 The interaction principle states that at least some mental events cause and are caused by physical events (Davidson 1970, 208). This leaves open the possibility of mental events that do not causally interact with physical events. However, given Davidson’s early views about event-individuation (the causal criterion) it is unclear that this possibility can be realized. His later views on event-individuation appear to leave this possibility open, but his general claims about the causal individuation of mental contents and attitudes (see  4.3  and  6.3  below) also stand in some tension with this possibility. In any case, Davidson goes on to say that he in fact believes that all mental events causally interact with physical events (Davidson 1970, 208), but he restricts his argument only to those that actually do. Given the pressures just noted in favor of the inclusive reading of the interaction principle, we shall assume it in what follows.