Causation, Metaphysics, and Our Understanding of the Natural World

For a long time, the slogan ‘there is a cause to everything’ was understood as an expression of the spirit of the scientifically informed mind, and an encapsulation of the belief that everything is naturally determined. The epistemic consequence of this belief is that we should seek natural explanations for all phenomena. In other words, the slogan expresses the belief that there is nothing haphazard or magical about the way the world is, and that therefore the world can be rationally understood. The idea that the world can be rationally understood doesn’t imply that the world follows the rules of the conceivable. I take it to be fairly clear that our imagination easily outstretches the restrictions imposed by the natural world. We can easily imagine Superman flying at three times the speed of light without having any idea of how to achieve thrust for that kind of speed, or without knowledge of what makes this factually impossible.

We can conceive of rime speeding up or slowing down, going backwards or what have you. And although an elucidation of what can and cannot be conceived is an important part of the project of finding out about the world (for instance, it can rule out options), then to find out what the world is actually like cannot only be an exploration of the conceivable. My idea of how to get closer to what the world is actually like is to confront some of the ways we can conceive it to be, with the theories and findings of the empirical sciences. They live under other constraints than the philosophical constraints of what can and cannot be conceived. They are obliged to confront what they conceive with what actually happens when we interact with the world, letting the outcome of those interactions rule out some of the ways we can conceive of the world.

To test philosophical theories against the theories and findings of the empirical sciences is not to let science dictate anything. The various empirical sciences have a narrow focus. Each investigates only a narrow segment of reality. Physics examines the smallest components and how they interact. Chemistry investigates larger compounds and how they react. Biology studies self-replicating compounds. Psychology studies conscious entities. Sociology studies groups of conscious entities. Nobody in these disciplines takes a step back to consider whether there are phenomena that cut across the segments each discipline studies. For instance, no physicist considers whether interactions between the particles they study are causal in the very same way reactions between chemical compounds are causal, or how monkeys peel bananas. That is a task only metaphysicians engage in. Obviously, physicists, chemists, and others can join in, but they can’t join in by doing more physics, chemistry, etc. They have to do metaphysics.

Now, however widespread the belief used to be that an understanding of causation is key to understanding the natural world, it is not universally accepted today that causation is a natural phenomenon. Indeed, for a couple of centuries the philosophical community has tended to favour approaches that reduce causation to some or other feature of how the world appears to us in experience, largely owing to the way our faculties of representation work, or of how we think about those features of experience, while avoiding speculation about what it is about the world that could make it appear to us in that way and therefore make our thoughts about it true. This is one of the senses in which philosophers understand themselves as ‘neo-Humeans’, i.e. as following the dictum that we should think of things only in terms of how they appear in experience while suspending judgement about how things really are. There is another kind of neo-Humeanism, one that doesn’t just suspend judgement but positively affirms that causation in the world is like it appears in experience, notably as a ‘mosaic of local matters of fact’, between which there are no substantial connections. So, there is both neo-Humean anti-realism and neo-Humean realism, although the resulting accounts of causation are practically indistinguishable; they only differ with respect to whether or not their proponents suspend judgement about whether their account of causation applies to reality or only to our way of thinking. It can be difficult to tell the difference. Both approaches can be seen in the writings of the same thinker. In his early writings, David Lewis only had the ambition to elucidate the ‘ordinary’ concept of causation, i.e. the way we ordinarily think (Lewis 1973«), while his later writings are more ontologically serious. In The Plurality of Worlds (1986«), Lewis postulates not only that people ordinarily think in terms of possible worlds (a claim that is up for debate), but that reality is actually made up of a plurality of worlds that are all equally existent and real.

Neo-Humeanism does trace its ancestry back to British empiricism, and we can see the same division in the empiricist tradition between realist and anti-realist empiricists. Hobbes (1656), Locke (1689), and J.S. Mill (1843) all believed that we acquire knowledge of the external world by deliberating on the input of the senses, although Mill suspended judgement about mysterious ties between the observable facts he took to be real. Berkeley (1709) and Hume (1739), however, argued that because all knowledge is confined to what our senses tell us, we can really only know something about the content of the mind. This split in the empiricist tradition is rarely brought out explicitly, and that carries over into contemporary neo-Humeanism. Realist neo-Humeans appropriate arguments from anti-realist empiricists for uses they were not originally meant to be used, assuming this to be of no consequence. As I will show in the next chapter, it does make a difference.

Although, arguably, realism dominated the empiricist thinking in the beginning, the dominant trend in 19th- and 20th-century philosophy has been to treat causation as merely a category of the mind, because it has been believed that the prospect of knowing what objective mindindependent reality is really like is hopeless. As a result, the philosophy of causation has predominantly aimed to reduce the notion of causation to some feature of how we think about causation, and/or some feature of experience that we accordingly identify with causation, rather than deliberating on whether such thinking is right or wrong in terms of accurately describing an objective feature of mind-independent reality, and/or why the world appears to us in experience in the way that it does. The current Aristotelian revival is a reaction to that trend.

The features of experience or of our thinking to which neo-Humeans have reduced causation so far, are regularity (Hume 1748; Graishoff & May 2001; Baumgartner 2008), necessary and/or sufficient conditions (Mill 1843; Mackie 1965), counterfactual dependence (Lewis 1973/?; Paul 1998; Hall 2000; Collins 2000), intervention (Gasking 1955; von Wright 1974; Menzies & Price 1993; Woodward 2003), and causal processes (Salmon 1984), the last often being complemented by an appeal to transmission accounts (Dowe 1992, 2009; Kistler 1998). Below, I’ll return to the details of these accounts.

It is not surprising that the shift from understanding causation as a form of natural determination to merely be a feature of cognition had the consequence that many of the features traditionally associated with natural determination have moved to the background. The philosophical community doesn’t seem to worry much today about the materialist principle that nothing comes into being out of nothing or is completely annihilated, wherefore there is no longer much focus on answering questions about the origin of the existing features of the world. Neo-Humeans are perfectly willing to postulate the brute existence of every physical state at every spacetime point from the beginning to end of time (and even of a plurality of worlds), without worrying about the question of how these states/worlds came to be. Indeed, even causal realists argue that the rejection of creation ex nihilo is just as much in need of justification as the claim that the world is recreated from nothing at every moment (Williams 2019: 213). Nor is there much focus on the idea that changes in the intrinsic properties of things only happen as a result of some influence being exerted by one thing on another. Indeed, Lewis can write a paper called ‘Causation as Influence’ (2000), elaborating on the notion of influence within a neo-Humean framework, without anyone objecting that the paper doesn’t say a single word about the influence exerted by anything on anything else. His talk of ‘influence’ reduces to talk about differences between worlds, which by definition cannot influence each other.

The idea that causation is a category of mind supports the validity of what is sometimes called armchair philosophy, i.e. types of reasoning that stays within the confines of our everyday conceptual scheme, and which takes the theories and findings of the empirical sciences to be irrelevant. Obviously, if we are only dealing with a conceptual category or feature of experience, then the empirical sciences—that profess to be about the way the world really works as opposed to how it appears to work—aren’t really relevant; we have all the access we want to the way we think from our armchair.

However, in the last two decades there has been a dramatically renewed interest in an engagement with the sciences, as a result, I believe, of the limitations of armchair philosophy with respect to deciding whether the way we think is right or wrong. As a result, contemporary realists have increasingly sought to re-evaluate the validity of the views of those thinkers of the past that took a naturalist approach and saw causation as a feature of the world. For a naturalist, the natural sciences provide important and relevant input for philosophical views. That kind of naturalist approach to metaphysics goes back to Aristotle, rather than to Plato, wherefore the Aristotelian tradition has naturally become a focal point of this movement. It bears to state already at this point that the main purpose of a re-evaluation of that kind is not primarily to arrive at a correct understanding of Aristotle. The main point is to consider whether there is something in his ideas that can be brought to bear today on how to understand causation. Some philosophers, Anna Marmodoro being one notable example, do a good job doing exegesis and constructive metaphysics at once (Marmodoro 2007, 2013). This book is an attempt to critically assess the progress of the causal realist revival, and to arrive at a view of causation that stands a better chance of being compatible with the theories and findings of natural science.

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