In Chapter 8 we examine Carl Craver’s well-known account of constitutive mechanisms, which takes the organised entities and activities that are the components of the mechanism to constitute the phenomenon to be explained. The main aim of the chapter is to criticise the adequacy of this view for illuminating mechanism as a concept-in-use in biological practice. We identify two main problems for the constitutive view: the problem of external components and the fact that some mechanisms can exist outside the entity the behaviour of which they underlie; we argue that both problems undermine the usefulness and appropriateness of viewing typical and paradigmatic cases of biological mechanisms in constitutive terms. The main claim of the chapter is that in order to understand the notion of mechanism as a concept-in-use, there is no need to posit a non-causal relation of constitution.

In Chapter 9 we present and defend a causal account of multilevel mechanistic explanation by examining various case studies from biology. We argue that two key consequences of Causal Mechanism are (1) that levels and mechanisms are distinct notions and (2) that levels of multilevel explanations are levels of composition. This view is in stark contrast to Craver’s account, according to which levels in multilevel explanations are levels of mechanisms and multilevel explanations are instances of constitutive explanations. A key claim of the chapter is that whatever contributes to the phenomenon is part of the same pathway; but causal pathways can contain entities from multiple levels of composition. In order to motivate and illustrate our view, we use various examples from biology and medicine. We criticise some common views associated with the picture of a hierarchy of mechanistic levels and argue that our view allows for causation at higher levels.