Periodic Reporting for period 3 - MetaScience (The Metaphysical Unity of Science) Reporting period: 2021-09-01 to 2023-02-28 Summary of the context and overall objectives of the project The Metaphysical Unity of Science ('MetaScience') project pursues the question of what, if anything, unifies the natural sciences. The project studies the question from the perspective of metaphysics and philosophy of science by way of employing case studies from biology, chemistry, and physics.What does it mean for one scientific phenomenon to be explained in terms of another? Under what conditions does scientific unification take place? In philosophy these questions are often discussed under the rubric of reduction. Typically, in asking whether one phenomenon reduces to another, we aim to understand what the ultimate or fundamental basis of the first phenomenon is. In the mid to late 20th century, there was a hope to reduce all higher level phenomena to fundamental physics. Yet, it was soon discovered that there are phenomena that cannot be easily reduced, so unification may not be available via this route.The project ’s ambitious goal is to produce a novel account of unification. This is made possible by recent breakthroughs in the methodology of metaphysics, an area sometimes called “metametaphysics”. The project’s objectives are:1. To establish the criteria for scientific unification2. To conduct case studies of actual scientific reductions at the biology-chemistry and the chemistry-physics interfaces3. To study the role of dependence relations weaker than reductionA cross-disciplinarily applicable toolbox for unification would be enormously useful for identifying the kind of expertise needed for understanding a given phenomenon. This is not merely a philosophical problem. If there are reasons to think that a given biological phenomenon reduces to chemical phenomena, then biologists studying that phenomenon had better be prepared to consult and collaborate with the chemists. If a unification can be achieved, we can determine when scientists ought to consult their colleagues in other sciences and also when this is likely to be a hindrance instead of an advantage. Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far So far, the team have examined numerous case studies concerning scientific unification as well as started developing new tools for assessing and formulating claims about scientific unification. There have been significant achievements on all three sub-projects (foundations, chemistry-physics interface, and biology-chemistry interface):For the foundations sub-project, the Unity of Science book (Tahko, Cambridge University Press, 2021) is a core reference work and analysis of the state of the art as well as open questions in this area. The book summarises the results from the first two years of the project and identifies foundational questions for the future, as well as giving an overview of some of the case studies conducted so far. In the meanwhile, the team have also been working on further explication of the key technical notions applied to the relevant case studies. These include relations of ontological dependence, reduction, realization, and emergence.On the chemistry-physics interface, important work has been done on the status of chemical bonds, molecular structure, and the role of the measurement problem in quantum chemistry. In particular, the possibility of emergence in these contexts has been analysed meticulously, with the result that some claims for strong emergence in this area may have been exaggerated, and there is a need for reinterpretation of these results with a more rigorous analysis of emergence. Further results in this area are expected shortly.On the biology-chemistry interface, an important pilot study was published early on, concerning the inter-level relationships at the interface between biology and chemistry, specifically, biochemical kinds such as proteins. These kinds pose interesting problems for philosophers of science, as they can be studied from the points of view of both biology and chemistry. A suggested upshot is that there are reasonable prospects for ontological reductionism about biochemical kinds, which corroborates natural kind monism. Further results in this area are also expected shortly, especially concerning the nature of functions and the status of genes. Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far) The project has proceeded largely as planned and has so far produced a wealth of knowledge on the present state of unity of science and related notions, such as emergence, reduction, and realization. Results going beyond the state of the art includes work both concerning the framework for unity of science in general as well as specific case studies which have so far been neglected or under-studied, e.g. the relationship of chemistry and biology in biochemical kinds and the status of molecular structure in chemistry.Future work involves further case studies, many of which are already under review, as well as further reference works. We also anticipate at least one further monograph, but depending on the project's developments there may be up to three further monographs, as well as an edited volume. Specific results that can already be anticipated or are being finalised concern work on natural kinds (specifically, the mind-independence criterion for kinds), the nature of chemical bonds, and the role of the measurement problem in quantum chemistry. We anticipate a steady flow of articles on these and other project themes in the coming years.