The chapter deals with the exclusion problem. How can mental events have physical effects if these effects already have physical causes? Even if this is possible in principle, would this not yield a situation like in a firing squad, where the victim’s death is overdetermined by the firings of the squad members? And would it not be implausible that the situation is like this whenever there is mental causation? If a difference-making approach to causation is adopted, these questions can be answered in a satisfactory way. Although mental and physical causes might nominally overdetermine their physical effects, cases of mental causation are sufficiently dissimilar to typical cases of overdetermination not to be problematic. Unlike in cases of mental causation (on the account offered here), in typical cases of overdetermination, the individual causes do not make a difference to the effect. The exclusion problem is harder to solve if it is formulated in terms of sufficient causes, but no commitment to sufficient causation follows from the account of mental causation in terms of difference-making.

The introduction describes the main problems of mental causation, their interrelations, and their history. The first problem is the interaction problem, the problem of how the mind and the physical world can interact at all. The second problem is the exclusion problem, the problem of how the mind can have physical effects given that these physical effects already have physical causes. How severe the problems are depends on the nature of the mind. The more intimate the relation between the mental and the physical, the more pressing the problems become. How severe the problems are also depends on the nature of causation. If causation requires the transference of a physical quantity, the problems are much harder to solve than if it suffices for causation if the cause makes a difference to the effect. The introduction outlines the history of the problems from Descartes to the twentieth century.