Metaphysicians, by and large, aim to be scientifically respectable in their theorizing. To what extent do they succeed? That’s an excellent question. But before we can answer it, we need to answer a more basic question: What does it mean to be scientifically respectable in your metaphysical theorizing, anyway?In this important and original book, Andreas Hüttemann puts forward a novel way of thinking about this second question. He puts forward, in other words, a novel methodology for naturalistic metaphysics. He then uses this methodology to generate a number of substantive metaphysical results regarding laws of nature, causation, and fundamentality. Although both aspects of the book—the methodological commitments and the metaphysical conclusions—are innovative, in what follows I will focus mainly on the former. One of the key claims I will make is that this methodology can be developed and deployed in more ways than one might at first recognize. That is to say, one can find inspiration in key aspects of Hüttemann’s methodology without endorsing the details of his metaphysics. (Though one may, of course, wish to endorse his metaphysics too.)Hüttemann’s methodology has two components: (1) a view about how to derive metaphysical commitments from scientific practice; and (2) a view about how to keep one’s metaphysics suitably minimal. The first component involves deploying the following schema:Practice to Metaphysics Schema1. Scientific practice includes X.2. The best explanation of the success of scientific practice, given that it includes X, is that metaphysical thesis M is true.3. So, M is true.As a particularly straightforward example, in chapter 1 Hüttemann argues that scientific practice includes using law statements to explain, confirm, and predict the behavior of systems. And the best explanation of the success of that practice is that systems exist. So, he concludes, systems exist. (Here systems are understood in contrast to the more traditional metaphysical category of substances. Systems can include everything from space-times to economies to hydrogen atoms.)So far, so good. As far as I am aware, the Practice to Metaphysics Schema has seen little if any discussion in the contemporary literature. (Perhaps the closest antecedents are indispensability arguments in philosophy of math a la Quine and Putnam.) The vast majority of discussions of naturalistic metaphysics have focused instead on the extent to which metaphysicians are respecting the content of our best scientific theories. But, as Hüttemann points out in the introduction, there are reasons to be skeptical of this focus. Perhaps most importantly, the content of our best scientific theories often undergoes dramatic changes when new theories are developed. Scientific practice, at least at a certain level of abstraction, appears to be more stable, maintaining the same general features even across periods of dramatic theory change.All of this is to say that the Practice to Metaphysics Schema seems like a fairly compelling route by which to pursue a naturalistic metaphysics. Indeed, I have trouble seeing how someone who calls themselves a naturalist could resist the conclusions generated by this schema, unless they have a good argument against relying on inference to the best explanation in general. At the same time, it seems pretty unlikely that the Practice to Metaphysics Schema as described above will place significant constraints on our metaphysical theorizing. This is because nothing has been said so far about how we are supposed to make judgments about which explanation is best. And as readers familiar with the literature are undoubtedly aware, there are many different ways of understanding what makes one explanation better than another.For this reason, it looks to me like the second component of Hüttemann’s methodology—the claim about minimality—is doing quite a lot of the work in generating the substantive metaphysical claims that he puts forward. And here, things do not seem quite so straightforward.Here is a natural way of understanding how minimality fits into the methodology after reading the introduction and first few chapters of the book. First one deploys the Practice to Metaphysics Schema. This is what makes one’s metaphysics a metaphysics of scientific practice. Then, one then applies the following criterion:This is what makes one’s metaphysics of scientific practice a minimal metaphysics of scientific practice.Here is an example that supports this reading. Later in chapter 1 (after the bit about systems), Hüttemann argues that nomological modality can be analyzed in terms of invariance relations. What it means to say that some pattern holds as a matter of nomological necessity, for instance, is just that it would continue to hold under various kinds of changes or interventions. (I’m rephrasing Hüttemann somewhat here, but I don’t think this matters for the point that I’m making.)Now, anyone who has spent time thinking about the metaphysics of laws, and certainly those of us who’ve been in the trenches of the Humean/anti-Humean debate will read this and think: well, that’s all fine, but now I want to know more about invariance. Hüttemann thinks we should resist this desire. He writes:As I read this passage, Hüttemann is saying: we have deployed the Practice to Metaphysics Schema, and it has told us to understand nomological modality in terms of invariance relations, but it hasn’t required us to take a stand on any further analysis of those relations. So following the Minimality Criterion, we should refuse to take such a stand. This isn’t to say that there is no further analysis of invariance relations or that they are primitive. Instead, a minimal metaphysics of scientific practice insists on remaining quiet regarding any further analysis of invariance relations.Insofar as this is a correct understanding of the role of minimality in Hüttemann’s methodology, it is clearly a further commitment that is independent of one’s commitment to the Practice to Metaphysics Schema. One could have a metaphysics of scientific practice, in Hüttemann’s sense, without endorsing a minimal metaphysics of scientific practice. And while I think someone who thinks of themselves as a naturalist will have a hard time resisting the Practice to Metaphysics Schema, I also think that they should feel free to resist the Minimality Criterion. One can take science to be a key, or even the best, source of information that we have about what the world is like while also thinking that there are some questions that science leaves open, and that it is fair game for metaphysicians to try to answer those open questions.The reader should note, however, that I am not entirely confident that the Minimality Criterion is the right way to think about the role of minimality in Hüttemann’s methodology. That things are more nuanced becomes clear in chapters 6–8, where Hüttemann considers the role of reductive explanation in scientific practice. (Hüttemann discuss a number of types of reductive explanation, but, as one example, consider the attempt to reductively explain the properties and behavior of thermodynamic systems in terms of the properties and behavior of corresponding statistical mechanical systems.)The key question that Hüttemann asks in these later chapters is which of the following three views best explains the success of scientific practice, given that scientific practice involves reductive explanation.I could write a whole second review on how to think about Ontologically Neutral Monism and the question of whether it is really an ontological or an epistemic thesis, as well as the details of why Hüttemann thinks that Ontologically Neutral Monism is capable of explaining the reductive aspects of scientific practice. But, for my purposes here, let’s just grant his argument that Ontologically Neutral Monism can do the relevant explanatory work, and let’s focus on his further claim that Ontologically Neutral Monism is a better explanation than either Physical Foundationalism or Physical Eliminativism. Here is what he writes in defense of this latter claim:This passage suggests that minimality is not a separate, secondary criterion but rather a key part of the Practice to Metaphysics Schema—minimality plays an important role in determining which explanation counts as the best explanation. The passage suggests, in other words, that we adopt the following criterion:According to this criterion, Ontologically Neutral Monism is a better explanation than either of the two competitors described above.The key point I want to make here, however, is that it still isn’t clear to me that there is any especially compelling reason for thinking that those committed to the Practice to Metaphysics Schema need to understand inference to the best explanation in terms of minimality. The Minimal-Explanation Criterion isn’t unreasonable, but it is also far from obvious. Someone could also reasonably argue that what is important in an explanation is that there is a certain degree of completeness in the information that it provides about the world—that it doesn’t leave obvious questions about the entities that it posits without an answer. One might, in other words, endorse the following criterion:And someone who endorses this criterion should presumably think that both Physical Foundationalism and Physical Eliminativism are better explanations than Ontologically Neutral Monism.So, to recap, although there are different ways of understanding the role that minimality plays in Hüttemann’s methodology. On either of the views discussed above, at least, minimality seems to be a commitment that a naturalist could well choose to resist.The foregoing remarks may sound critical, but I don’t think they should be read that way. The key thing to take away from all this is that a metaphysics of scientific practice, by which I mean a metaphysics that relies crucially on Hüttemann’s Practice to Metaphysics Schema, can be developed in a range of different ways that, almost certainly, will give rise to many different metaphysical views. And this speaks to the fact that this book can—and should!—have both a broad and long-lasting impact. Even those who disagree with the details of Hüttemann’s metaphysical views or his arguments for those views should pay close attention to the innovative methodology he is proposing.