Anyone interested in the topic of causal mechanisms will be interested in the appearance of Stuart Glennan and Phyllis Illari's The Routledge Handbook of Mechanisms and Mechanical Philosophy. Both Glennan and Illari have been significant contributors to the past fifteen years of discussion about the role of mechanisms in scientific explanation, and the Handbook is a highly interesting contribution to the state of the debate.
The book provides discussion of the role of mechanisms thinking in a wide range of scientific disciplines, from physics to biology to social science to engineering and cognitive science. It consists of four large sections: "Historical perspectives on mechanisms", "The nature of mechanisms", "Mechanisms and the philosophy of science", and "Disciplinary perspectives on mechanisms." Each section consists of contributions by talented experts on genuinely interesting topics.
A good introduction to the general topic of mechanisms is the introduction to the volume by Glennan and Illari, and more especially their article, "Varieties of mechanisms." They directly confront one of the large issues in the field, the wide dispersion of definitions and applications of the idea of a causal mechanism. They correctly observe that the concept of mechanism is used fairly differently in various areas of science and philosophy, but they argue that there is a common core of elements that underlie most or all of these usages. The variety that exists is the result of differences in the nature of the phenomena across different areas of scientific investigation, and differences in methodology in use in various sciences. They provide a rather general definition of a mechanism:
A mechanism for a phenomenon consists of entities (or parts) whose activities and interactions are organized so as to be responsible for the phenomenon. (92)They then attempt to provide a basis for classifying different kinds of mechanisms according to several different criteria. The dimensions of variation they identify include the kind of phenomenon produced, the kind of entities and activities constituting the mechanism, the way in which entities and activities are organized, and the etiology of the mechanism.
Also interesting is Petri Ylikoski's contribution, "Social mechanisms." Ylikoski structures his exposition of the theory of social mechanisms around the Coleman boat diagram (link). To provide a mechanism for a social phenomenon is to provide an account at the level of the actors of how a macro-level event or entity causally brings about another macro-level event or entity. Ylikoski insists that this is a matter of explanatory adequacy rather than reductive analysis, and is therefore not ontologically reductionist. But it does fundamentally imply that social mechanisms occur at the level of interactions among actors. In prior posts I have argued against this presupposition (link). I argue that it is perfectly intelligible to suggest that there are meso-level causal mechanisms. Ylikoski also underlines the affinity that exists between social mechanisms and agent-based modeling: a good ABM demonstrates the process through which a set of conditions at the micro-level aggregate to a certain kind of macro-level outcome. See this earlier post for a small amount of doubt about the adequacy of ABM models to perform this kind of social aggregation for realistic social scenarios; link. (Several of these points are developed in my New Directions in the Philosophy of Social Science.)
Povich and Craver address the topic of the relationship that exists between mechanisms, levels, emergence, and reduction in their contribution, "Mechanistic levels, reduction, and emergence". This is a key question within the philosophy of social science. And the idea of mechanism seems to have great relevance to the idea of various levels of phenomena. At the level of the organization we see, perhaps, chronic inefficiency in the use of certain kinds of resources. In searching for the mechanisms that cause this inefficiency we may choose to drop down a level and examine the incentives and constraints that guide the behavior of individuals within the organization. And we arrive at a theory of the individual-level mechanism that produces the meso-level outcome. This is a mechanism that falls along strut 3 of Coleman's boat; it is an aggregative mechanism. But not all social mechanisms have this nature. If we want to know why rebellious segments of an agrarian society locate themselves in remote, mountainous areas, it is enough to know a few meso-level facts about the functioning of traditional military forces and the meso-level fact that mountainous terrain gives a tactical advantage to rebel commanders. This appears to be a meso-level mechanism from start to finish.
A particularly intriguing and original contribution is Abrahamsen, Sheredos, and Bechtel's "Explaining visually using mechanism diagrams." We tend to think of scientific explanations as mathematical demonstrations or text-based derivations of outcomes. Abrahamsen, Sheredos, and Bechtel point out that visual diagrams play a crucial role in the presentation of many scientific results; and these diagrams are not merely heuristic or illustrative. A visual presentation serves to designate how the hypothesized mechanism works: what its parts are, how the parts influence each other, and how the functioning of the mechanism over time produces the outcome in question. The authors make an admirable attempt to provide a philosophy-of-science analysis of the components and logic of a visual diagram as an expository device for presenting a causal mechanism or process. They highlight the logical problems of representing entities, spatial location, and temporal duration within a diagram in a way that permits the viewer to gain an accurate understanding of the hypothesized mechanism or process. And they note that it is a conceptually simple step to introduce computational modeling into the graphical representation described here, so the processes in question can step through their interactions on-screen.
Taken together, the essays collected here constitute a valuable contribution to the literature on mechanisms and explanation. The handbook also gives the reader a concrete experience of how deeply varied the mechanisms literature is, leading to very interesting questions about cross-disciplinary communication. It appears to be genuinely challenging to formulate an abstract analysis of the idea of a causal mechanism that will mean approximately the same thing to researchers trained within significantly different research traditions. Unlike many handbooks, this collection warrants reading cover to cover. Researchers who believe that the mechanisms approach provides a valid way of understanding the metaphysics of causal inquiry and explanation will find every article stimulating and helpful.
(Here are a couple of prior posts on the challenge of providing a classification scheme for social mechanisms; link, link.)