Ontology and the Foundations of Mathematics

This Element looks at the problem of inter-translation between mathematical realism and anti-realism and argues that so far as realism is inter-translatable with anti-realism, there is a burden on the realist to show how her posited reality differs from that of the anti-realist. It also argues that an effective defence of just such a difference needs a commitment to the independence of mathematical reality, which in turn involves a commitment to the ontological access problem – the problem of how knowable mathematical truths are identifiable with a reality independent of us as knowers. Specifically, if the only access problem acknowledged is the epistemological problem – i.e. the problem of how we come to know mathematical truths – then nothing is gained by the realist notion of an independent reality and in effect, nothing distinguishes realism from anti-realism in mathematics.

Invariance as a basis for necessity and laws

Many philosophers are baffled by necessity. Humeans, in particular, are deeply disturbed by the idea of necessary laws of nature. In this paper I offer a systematic yet down to earth explanation of necessity and laws in terms of invariance. The type of invariance I employ for this purpose generalizes an invariance used in meta-logic. The main idea is that properties and relations in general have certain degrees of invariance, and some properties/relations have a stronger degree of invariance than others. The degrees of invariance of highly-invariant properties are associated with high degrees of necessity of laws governing/describing these properties, and this explains the necessity of such laws both in logic and in science. This non-mysterious explanation has rich ramifications for both fields, including the formality of logic and mathematics, the apparent conflict between the contingency of science and the necessity of its laws, the difference between logical-mathematical, physical, and biological laws/principles, the abstract character of laws, the applicability of logic and mathematics to science, scientific realism, and logical-mathematical realism.

Mathematical Indispensability and Arguments from Design

The recognition of striking regularities in the physical world plays a major role in the justification of hypotheses and the development of new theories both in the natural sciences and in philosophy. However, while scientists consider only strictly natural hypotheses as explanations for such regularities, philosophers also explore meta-natural hypotheses. One example is mathematical realism, which proposes the existence of abstract mathematical entities as an explanation for the applicability of mathematics in the sciences. Another example is theism, which offers the existence of a supernatural being as an explanation for the design-like appearance of the physical cosmos. Although all meta-natural hypotheses defy empirical testing, there is a strong intuition that some of them are more warranted than others. The goal of this paper is to sharpen this intuition into a clear criterion for the (in)admissibility of meta-natural explanations for empirical facts. Drawing on recent debates about the indispensability of mathematics and teleological arguments for the existence of God, I argue that a meta-natural explanation is admissible just in case the explanation refers to an entity that, though not itself causally efficacious, guarantees the instantiation of a causally efficacious entity that is an actual cause of the regularity.

The Honest Weasel A Guide for Successful Weaseling

Indispensability arguments are among the strongest arguments in support of mathematical realism. Given the controversial nature of their conclusions, it is not surprising that critics have supplied a number of rejoinders to these arguments. In this paper, I focus on one such rejoinder, Melia’s ‘Weasel Response’. The weasel is someone who accepts that scientific theories imply that there are mathematical objects, but then proceeds to ‘take back’ this commitment. While weaseling seems improper, accounts supplied in the literature have failed to explain why. Drawing on examples of weaseling in more mundane contexts, I develop an account of the presumption against weaseling as grounded in a misalignment between two types of commitments. This is good news to the weasel’s opponents. It reinforces that they were right to question the legitimacy of weaseling. This account is also beneficial to the weasel. Uncovering the source of the presumption against weaseling also serves to draw out the challenge that the weasel must meet to override this presumption—what is required to be an ‘honest weasel’.

Realism, Ontology, and Objectivity

This chapter explicates the concept of realism, and distinguishes it from related concepts with which it is often conflated. It shows that, properly conceived, realism has no ontological implications, and that influential epistemological objections to moral and mathematical realism fallaciously assume otherwise. One upshot of the discussion is that it is no response to Paul Benacerraf’s epistemological challenge to claim that there are no special mathematical entities with which to “get in touch.” The chapter concludes with a distinction between realism and objectivity, a distinction which is central to Chapter 6. It uses the Parallel Postulate, understood as a claim of pure geometry, as a paradigm of a claim that fails to be objective, even if mathematical realism is true. Conversely, it explains how realism about claims of a kind may be false even though they are objective in a sense in which the Parallel Postulate is not.

Morality and Mathematics

This book explores arguments for and against moral realism and mathematical realism, how they interact, and what they can tell us about areas of philosophical interest more generally. It argues that our mathematical beliefs have no better claim to being self-evident or provable than our moral beliefs. Nor do our mathematical beliefs have better claim to being empirically justified. It is also incorrect that reflection on the “genealogy” of our moral beliefs establishes a lack of parity between the cases. In general, if one is a moral anti-realist on the basis of epistemological considerations, then one ought to be a mathematical anti-realist too. And yet, the book argues that moral realism and mathematical realism do not stand or fall together – and for a surprising reason. Moral questions, insofar as they are practical, are objective in a sense in which mathematical questions are not, and the sense in which they are objective can only be explained by assuming practical anti-realism. It follows that the concepts of realism and objectivity, which have been widely identified, are actually in tension. The author concludes that the objective questions in the neighborhood of questions of logic, modality, grounding, nature, and more are practical questions as well. Practical philosophy should, therefore, take center stage.

Realism, Objectivity, and Evaluation

This chapter discusses “realist pluralism” in mathematics and morality. It argues that, under the assumption of pluralism, factual questions get deflated while practical -- i.e., what-to-do -- questions do not. It then uses this contrast to formulate a radicalization of Moore’s Open Question Argument. Practical questions remain open even when the facts, including the evaluative facts, come cheaply. The chapter concludes that practical realism must be false, but practical questions are objective in a paradigmatic respect. Conversely, mathematical realism is true, but mathematical questions fail to be objective. An important upshot of the discussion is that the concepts of realism and objectivity, which are widely identified, are actually in tension.