In Chapter 4 we build on the discussion in Chapter 3 in order to argue that understanding mechanisms in the Causal Mechanism sense is all that is needed in order to understand biological practice. We clarify the main commitments of our view by presenting three theses that together constitute Causal Mechanism: (1) Mechanisms are to be identified with causal pathways; (2) causal relations among the components of a pathway are to be viewed in terms of difference-making; and (3) Causal Mechanism is metaphysically agnostic. A key point is that, in contrast to mechanistic theories of causation, for Causal Mechanism causation as difference-making is conceptually prior to the notion of a mechanism. We examine in some detail the discovery of the mechanism of scurvy in order to argue that difference-making is what matters in practice. We then turn to the main inflationary accounts of mechanism and contrast them with our deflationary view and its metaphysical agnosticism. We argue that Causal Mechanism offers a general characterisation of mechanism as a concept-in-use in the life sciences that is deflationary and thin, but still methodologically important.

The Introduction recounts the main aspects of the recent revival of the mechanical philosophy and outlines the main theses of the book (i.e., Causal Mechanism and Methodological Mechanism). It presents briefly the case for understanding mechanism as a methodological concept, introduces the main concepts and distinctions that will be discussed in the book, provides an outline of the central arguments and presents a summary of the chapters.

In Chapter 6, we defend the difference-making thesis of Causal Mechanism, that is, the view that mechanisms are underpinned by networks of difference-making relations, by showing that difference-making is more fundamental than production in understanding mechanistic causation. Our argument is two-fold. First, we criticise Stuart Glennan’s claim that mechanisms can be viewed as the truth-makers of counterfactuals and argue that counterfactuals should be viewed as metaphysically more fundamental. Second, we argue against the view that the productivity of mechanisms requires thinking of them as involving activities, qua a different ontic category. We criticise two different routes to activities: Glennan’s top-down approach and Phyllis Illari and Jon Williamson’s bottom-up approach. Given these difficulties with activities and mechanistic production, it seems more promising to start with difference-making and give an account of mechanisms in terms of it.

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.