  This version of the problem has dogged dualism since the scientific revolution (Lowe 1992; Papineau 2000), and a number of contemporary philosophers present conservation as a major obstacle for dualists (Fodor 1981; Dennett 1991, p. 35; Heil 2012, p. 26). That said, turning the leading idea into a compelling argument has proven difficult. First, what is needed is a conservation law weak enough to have been confirmed by physical science, but strong enough to preclude soul–body interaction. Averill and Keating (1981) consider a number of candidate “laws” and argue that none meets both criteria. Second, it’s not clear in any case that a soul would have to add energy to (or receive it from) the brain in order to interact with it. The transference theory (§2.1) again seems to be in the background here, but why accept it? Broad (1925, pp. 103–9) suggests a soul could act merely by redistributing the brain’s energy without changing its quantity. (For more recent discussion of these and other complexities, see Montero 2006; Koksvik 2007; Gibb 2010.)