Part III Ontological Consequences In Part III I focus on how the structure of chemistry as a network of theories connected by links has a bearing on the ontology of chemistry. The guiding principle in this part of the book is that – perhaps due to my history as a practicing scientist – I find it impossible to see how we can sensibly talk about realism and ontology without an explicit understanding of the science that lies in front of it. Much of the writing on the ‘metaphysics side’ of philosophy strikes me as expensive grandstanding on the basis of folk-science. As you sometimes hear at conferences: ‘butsurelyitmustbethecasethat...’ Frommyperspective, whether something really is the case or not is a matter of science rather than intuition. So I lay some explicit cards on the table first: ‘ontology’ in my view is best seen as the end-result of extensional quantification over suitably formalised mature theories, and not as something that one can ‘a priori’ determine and then impose. In this view, the idea that there is some ‘ontology’ that is ‘prior’ to theories is really tantamount to choosing intuitive theories of nature over scientifically robust ones. As a matter of taste and ethics, it is ‘not done’ to for philosophers of science to lecture or critique scientists on this basis. My overall approach is that I argue for a strongly ‘naturalised’ epistemology for the philosophy of chemistry in the sense that ontological arguments follow, generally through a process of ontological commitment and ontological grounding, from epistemic arguments rather than being prior to them. This finally touches on a topic that in my view needlessly confuses many otherwise fine philosophers of chemistry: ontological reduction. My proposal is that the problems around ontological reduction are best solved in the context of ontological commitment in combination with a notion of ‘grounding’. On the view that theories are ontologically committed to their theoretical entities and have a grounding relation to other entities, ontological reduction becomes a function of epistemological reduction. This somewhat austere view on ontology allows us to critically evaluate the notion of ‘ontological reduction’. 232 III Ontological Consequences Summary of Part III In this part, I have explored the ontological consequences of the formal models developed in Part II. I have thereby adhered to a rather strict operational interpre- tation of ontology: the quantification over suitable formal paraphrases of actual theories. This is a scientists’ approach, and alternative approaches are possible. From my point of view, however, these still amount to the same thing: building a chemical ontology on top of, for instance, a mereological framework still entails a subscription to a theory about what is part of what. while such theories are often seen as self-evident or not in need of further defence, in my opinion in practice they may vary rather a lot in how well they are empirically supported. While it might certainly be possible to come to some results this way, I far prefer the road that leads from actual, empirically supported theories to ontological entities. The problem, which I have merely outlined in this part, is that when it comes to theories of chemistry not only the actual existence of such theories might be in doubt, but moreover, in cases where such theories can specified with sufficient precision, they are highly complex networks of theories, joined by links that are in turn highly selective in the amount and nature of information they convey from one part to the other. I have argued that such a situation is problematic for some highly simplified theories of ontology, but should be welcomed by those philosophers who argue for more refined models of ontology, such as rainforest realism, ‘depth’ or engineering. And these may not be the only alternatives. There may be more philosophy to be had. I firmly believe that the future of philosophy of chemistry lies not in rehashing the old arguments around reference, hard realism or complex arguments based on the quantification of intuitively attractive but ultimately weakly supported notions of what ‘surely must be the case’. The future, if it is to be fruitful, will have to consider empirically supported theories of chemistry in their full complexity and pair this with a suitable notion of what a chemical object looks like. In the end, ontologists will just have to learn to put up with that..