Does the no general structure thesis count as significant metaphysics?
Does the claim that the world lacks a general, overall structure that spans scales count as a significant metaphysical idea? I close this chapter by responding to four objections to the supposition that it does. But before proceeding with the first objection, it is worth pointing out that a denial of a metaphysical thesis is itself a metaphysical thesis. The assumption that the world has a “the structure” across scales, which is widely held by philosophers of science, is a metaphysical thesis. Hence, claims that deny this assumption are also metaphysical. So the claim that the reality within organisms lacks an overall structure at the scale at which geneticists engage, and more generalized versions of this claim, must also be metaphysical.
Objection 1: The no general structure thesis is too skeptical to count as metaphysics. After all, it amounts to an antirealist view about science, so it must be anti-metaphysics.
This chapter does not advance an antirealist view of science. Section 3 sketches classical geneticists’ explanations of phenotypic transmission patterns for two purposes. The first purpose is to show that the theoretical explanations of classical genetics  
have stood the test of time. We should be realists about the geneticists’ theoretical claims that gene differences caused phenotypic differences in the experimental contexts they constructed and that patterns of phenotypic transmission produced in experiments resulted from the transmission of gene differences from one generation to the next. Classical geneticists were right about the causal relationship between genotype and phenotype in their experiments, they were right about gene differences being located in linear fashion in chromosomes, and they were right about the roles that chromosomal mechanics in meiosis played in producing the patterns of gene transmission they produced in the laboratory.
The second purpose for sketching the theoretical explanations in classical genetics is to separate this realist account of the transmission theory from a fundamentalist interpretation of this theory (the former is presented in section 3, the latter in section 4). I agree with Cartwright (1999, 23) that fundamentalism, not realism, is the problem.
We should also be realists about the central theory of contemporary genetics, but again we should separate our realism from a fundamentalist interpretation of the theory. Scientific metaphysics should proceed from an analysis of the form that practice in genetics takes, not from an analysis of its core theoretical concepts removed from the context of that practice. Simply put, metaphysics should be practice centered, not theory focused. But practice-centered metaphysics does not ignore theory, and it does not adopt an anti-realist attitude toward those theories. Hence, this metaphysics is not based on antirealism.
Objection 2: Can we really draw a conclusion about metaphysics from scientific practice ? Does not this analysis simply reveal epistemological or cognitive limitations ?
This objection expresses a worry that applies to all metaphysics. When metaphysicians employ methods of analytic philosophy to investigate how the world must be, might they just be investigating how we must conceive the world because of our cognitive limitations ? When traditional, scientific metaphysicians interpret the theories and explanations of physics to investigate “the structure” of the world, might they just be reinforcing scientists’ biases or theories that are partly shaped by our limited cognitive abilities? Might the apparent mess of causal interactions within organisms being investigated using genetics have an overall structure that humans cannot recognize because of cognitive limitations ? Yes, yes, and yes.
Metaphysics is risky business. Scientific metaphysics is based on the idea that appealing to science to inform metaphysics will decrease the risks. Appealing to a broader analysis of science, one that examines the use of concepts and theories in the context of investigative, manipulative, and local explanatory practices will better inform metaphysics. I maintain that informing metaphysics by analyzing the concepts and theories of science from a narrow, theory-focused perspective is riskier than informing metaphysics by analyzing the investigative and manipulative practices in which these concepts and theories are employed.
Objection 3: This conclusion is not sufficiently general to count as metaphysics.
A preliminary response to this objection is given in section 2. But it is worth restating with respect to the no general structure thesis. A critic advancing this objection might be willing to grant that the causal processes within an organism lack an overall structure at the scale at which geneticists engage. But the critic could still object, “So what if the world at this scale within organisms is a mess? This does not mean that the nonliving world at this scale is a mess (scope issue). And it does not even mean that the world within the organism is a mess (scale issue). To determine whether the world is a mess, one needs to consider everything in the whole world, not just some entities within it (organisms). And to consider the world at this universal scope, one must consider it at the appropriate scale, a much smaller scale than the scale of causal interaction being investigated by geneticists. Fundamental physics is the only discipline that can reveal whether the world has an overall structure and what that structure might be.”
In section 2, I respond to this kind of objection by suggesting that we should adopt a different sense of general. Instead of thinking of general in terms of applying to everything at some one scale, we should conceive of generality across different scales. Claims about an overall structure existing at very small scales are not necessarily informative about whether there are overall structures at larger scales. The generality across scales thesis suggests that the no overall structure idea applies quite generally across scales being investigated by biological and social scientists, and by physical scientists in many fields as well. Metaphysics can (and should) be thought of as concerning what is true across many scales, especially across scales we directly engage and experience as human beings.
Objection 4: This conclusion does not count as a significant metaphysical thesis because it is trivial.
Stanford (this volume, chap. 6) critiques traditional scientific metaphysics and argues that it adds nothing of value to philosophy of science. I believe Stanford’s critique raises an important question: what is scientific metaphysics good for? Being informed by science, by itself, does not make a metaphysics important. Metaphysics should not only be informed by science; metaphysics should be informing science, the rest of philosophy, and society as well. I conclude this chapter by arguing that the no general structure thesis is a metaphysical doctrine of real importance.
With respect to philosophy, the no general structure thesis can inform our epistemology of science. Consider philosophy of biology. This thesis implies that the questions set out in section 2 should not be interpreted as fundamental questions. The distinction drawn with respect to classical genetics should be drawn with respect to these questions as well. In the case of classical genetics, the science provided accurate descriptions and explanations, but it should not be interpreted to yield a fundamental account of heredity, development, or evolution. Such interpretations rest on an assumption that the processes of heredity, development, and evolution have some fundamental structure such that it must be possible to find a basis of scientific understanding that keys into that structure. But the no general structure thesis implies that our interpretations of scientific knowledge should not be premised on the faith that such structures exist. This thesis has important implications for how philosophers of biology should interpret and answer questions such as “what is a species?" “what is an organism?" or “what is a Darwinian population?" In addition, the no general structure thesis has implications for how we should interpret and answer meta-scientific questions such as “what is a natural kind?"
The no general structure thesis can inform science as well. The quest for a comprehensive and unified, or even integrated, explanatory perspective can be a useful heuristic, but it should be viewed as a heuristic, not as the aim of science. Practicing geneticists were right not to follow philosophers when we obsessed about questions such as “what is fitness?" or “what is a gene?" It might be heuristically useful to ask such questions, but when it is not useful, such questions can simply be dropped and the project of investigating and manipulating nature can resume. A philosophy of biology that asked, “What ways of conceiving of biological individuals could be useful?" and “in what contexts and for what purposes would they be useful?" would be much more informative to biologists than simply asking, “What is a biological individual?." The no general structure thesis is important to science. A philosophy of science that adopted this thesis would be more useful to scientists.
The no general structure thesis is far from trivial. It has important implications for how scientists should conduct their investigations and how we (philosophers of science) should conduct ours. But should not metaphysics do more ? Should it not also inform society about how to conduct its affairs ? The no general structure thesis can deliver on this desideratum as well. It suggests that society should admire science for its secure knowledge about the world, but that society should not interpret that knowledge as if it depended upon or provided an understanding of fundamentals.
Research in genetics should be supported and funded, but not because it will “decode life” or reveal the magic keys to unlocking solutions to the complex problems societies face. The no general structure thesis applies generally across scales at which we experience the world. It has implications for how philosophers should understand scientific knowledge and for how scientists construct such knowledge. And it can inform the public understanding, support, and use of science. Such a thesis counts as significant metaphysics.
-  15 The significance of the idea that the science of fundamental physics “holds” across scales, often expressed byphilosophers of physics (e.g., Ladyman, this volume, chap. 7), is unclear. Does it imply that the laws or principles of fundamental physics structure the world across scales? This depends upon how we interpret ‘holds.’
-  believe there is a way to interpret the idea that a set of principles “holds across scales” that is consistent withthe no generality across scales thesis. This is an idea worth exploring, but I do not have the space to do so here.
-  ; For more on the distinction between practice-centered and theory-focused, see Waters 2014.