According to modal realism formulated by David Lewis, there exist concrete possible worlds. As he argues the hypothesis is serviceable and that is a sufficient reason to think it is true. On the other side, Lewis does not consider the pragmatic reasons to be conclusive. He admits that the theoretical benefits of modal realism can be illusory or that the acceptance of controversial ontology for the sake of theoretical benefits might be misguided in the first place. In the first part (...) of the paper, I consider the worry and conclude that although the worry is justified, there can be an epistemological justification for his theory. Next, I outline the so-called indispensability argument for the legitimacy of mathematical Platonism. Finally, I argue that the argument, if accepted, can be applied to metaphysics in general, to the arguing for the existence of concrete (im)possibilia in particular. (shrink)

There is a wide range of realist but non-Platonist philosophies of mathematics—naturalist or Aristotelian realisms. Held by Aristotle and Mill, they played little part in twentieth century philosophy of mathematics but have been revived recently. They assimilate mathematics to the rest of science. They hold that mathematics is the science of X, where X is some observable feature of the (physical or other non-abstract) world. Choices for X include quantity, structure, pattern, complexity, relations. The article lays out and compares these (...) options, including their accounts of what X is, the examples supporting each theory, and the reasons for identifying the science of X with (most or all of) mathematics. Some comparison of the options is undertaken, but the main aim is to display the spectrum of viable alternatives to Platonism and nominalism. It is explained how these views answer Frege’s widely accepted argument that arithmetic cannot be about real features of the physical world, and arguments that such mathematical objects as large infinities and perfect geometrical figures cannot be physically realized. (shrink)

This volume explores the inadequacies of the two standard conceptions of space or spacetime, substantivalism and relationism, and in the process, proposes a new historical interpretation of these physical theories. This book also examines and develops alternative ontological conceptions of space, such as the property theory of space and emergent spacetime hypotheses, and explores additional historical elements of seventeenth century theories and other metaphysical themes. Readers will learn about specific problems with the substantivalism versus relationism dichotomy. First, Newton and Leibniz (...) are often upheld as the retrospective forerunners of, respectively, substantivalism and relationism, but their work often contradicts the central tenets of these views. Second, these theories have proven problematic when transferred to a modern setting, especially with regards to general relativity and the recent quantum gravity hypotheses. In order to address these problems, the author develops a new classificational system that provides a more accurate taxonomy for the elements of all spatial ontologies, both in the seventeenth century and for contemporary theories of physics. This classification obtains successful analogies between Newton, Leibniz, and other natural philosophers with contemporary physical theories, and it also admits a role for the current brand of emergent spacetime hypotheses and the property theory of space. (shrink)

The semantic view of theories is normally considered to be an ac-count of theories congenial to Scientific Realism. Recently, it has been argued that Ontic Structural Realism could be fruitfully applied, in combination with the semantic view, to some of the philosophical issues peculiarly related to bi-ology. Given the central role that models have in the semantic view, and the relevance that mathematics has in the definition of the concept of model, the fo-cus will be on population genetics, which is (...) one of the most mathematized areas in biology. We will analyse some of the difficulties which arise when trying to use Ontic Structural Realism to account for evolutionary biology. (shrink)