Online research in philosophy

Fictionalism in the philosophy of mathematics is the view that mathematical statements, such as ‘8+5=13’ and ‘π is irrational’, are to be interpreted at face value and, thus interpreted, are false. Fictionalists are typically driven to reject the truth of such mathematical statements because these statements imply the existence of mathematical entities, and according to fictionalists there are no such entities. Fictionalism is a nominalist (or anti-realist) account of mathematics in that it denies the existence of a realm of abstract mathematical entities. It should be contrasted with mathematical realism (or Platonism) where mathematical statements are taken to be true, and, moreover, are taken to be truths about mathematical entities. Fictionalism should also be contrasted with other nominalist philosophical accounts of mathematics that propose a reinterpretation of mathematical statements, according to which the statements in question are true but no longer about mathematical entities. Fictionalism is thus an error theory of mathematical discourse: at face value mathematical discourse commits us to mathematical entities and although we normally take many of the statements of this discourse to be true, in doing so we are in error (cf. error theories in ethics).

The question posed in the title of this paper is an historical one. I am not, for example, primarily interested in the term 'Platonism' as used by modern philosophers to stand for a particular theory under discussion – a theory, which it is typically acknowledged, no one may have actually held.1 I am rather concerned to understand and articulate on an historical basis the core position of that 'school' of thought prominent in antiquity from the time of the 'founder' up until at least the middle of the 6th century C.E.2 Platonism was unquestionably the dominant philosophical position in the ancient world over a period of more than 800 years. Epicureanism is perhaps the sole major exception to the rule that in the ancient world all philosophers took Platonism as the starting-point for speculation, including those who thought their first task was to refute Platonism. Basically, Platonism sent the ancient philosophical agenda. Given this fact, understanding with some precision the nature of Platonism is obviously a desirable thing for the historian of ancient philosophy.

Platonism about mathematics (or mathematical platonism) is the metaphysical view that there are abstract mathematical objects whose existence is independent of us and our language, thought, and practices. In this survey article, the view is clarified and distinguished from some related views, and arguments for and against the view are discussed.

The goal is to sketch a nominalist approach to mathematics which just like neologicism employs abstraction principles, but unlike neologicism is not committed to the idea that mathematical objects exist and does not insist that abstraction principles establish the reference of abstract terms. It is well-known that neologicism runs into certain philosophical problems and faces the technical difficulty of finding appropriate acceptability criteria for abstraction principles. I will argue that a modal and iterative nominalist approach to abstraction principles circumvents those difficulties while still being able to put abstraction principles to a foundational use.

Daft. Berkeley denied the existence of abstract ideas and any faculty of abstraction. At the same time, however, he embraced innate ideas and a faculty of pure intellect. This paper attempts to reconcile the tension between these commitments by offering an interpretation of Berkeley's Platonism.

Current versions of nominalism in the philosophy of mathematics have the benefit of avoiding commitment to the existence of mathematical objects. But this comes with the cost of not taking mathematical theories literally. Jody Azzouni's Deflating Existential Consequence has recently challenged this conclusion by formulating a nominalist view that lacks this cost. In this paper, we argue that, as it stands, Azzouni's proposal does not yet succeed. It faces a dilemma to the effect that either the view is not nominalist or it fails to take mathematics literally. After presenting the dilemma, we suggest a possible solution for the nominalist.

Mark Balaguer's Platonism and Anti-Platonism in Mathematics presents an intriguing new brand of platonism, which he calls plenitudinous platonism, or more colourfully, full-blooded platonism. In this paper, I argue that Balaguer's attempts to characterise full-blooded platonism fail. They are either too strong, with untoward consequences we all reject, or too weak, not providing a distinctive brand of platonism strong enough to do the work Balaguer requires of it.

If anything is taken for granted in contemporary metaphysics, it is that platonism with respect to a discourse of metaphysical interest, such as fictional or mathematical discourse, affords a better account of the semantic appearances than nominalism, other things being equal. This belief is often motivated by the intuitively stronger one that the platonist can take the semantic appearances “at face-value” while the nominalist must resort to apparently ad hoc and technically problematic machinery in order to explain those appearances away.

In this paper, I argue that, on any natural construal of “face-value”, the platonist, like the nominalist, does not in general seem to be able to take the semantic appearances at face-value. And insofar as the nominalist is forced to adopt apparently ad hoc and technically problematic machinery in order to explain those appearances away, the platonist is generally forced to adopt machinery which is at least prima facie ad hoc and technically problematic as well. One moral of the story is that the thesis that platonism affords a better account of the semantic appearances than nominalism, other things being equal, is not trivial. Another is that we should rethink our methodology in metaphysics.

In this book, Balaguer demonstrates that there are no good arguments for or against mathematical platonism. He does this by establishing that both platonism and anti-platonism are defensible views. Introducing a form of platonism ("full-blooded platonism") that solves all problems traditionally associated with the view, he proceeds to defend anti-platonism (in particular, mathematical fictionalism) against various attacks, most notably the Quine-Putnam indispensability attack. He concludes by arguing that it is not simply that we do not currently have any good argument for or against platonism, but that we could never have such an argument and, indeed, that there is no fact of the matter as to whether platonism is correct.

If anything is taken for granted in contemporary metaphysics, it is that platonism with respect to a discourse of metaphysical interest, such as fictional or mathematical discourse, affords a better account of the semantic appearances than nominalism, other things being equal. This belief is often motivated by the intuitively stronger one that the platonist can take the semantic appearances “at face-value” while the nominalist must resort to apparently ad hoc and technically problematic machinery in order to explain those appearances away.

In this paper, I argue that, on any natural construal of “face-value”, the platonist, like the nominalist, does not in general seem to be able to take the semantic appearances at face-value. And insofar as the nominalist is forced to adopt apparently ad hoc and technically problematic machinery in order to explain those appearances away, the platonist is generally forced to adopt machinery which is at least prima facie ad hoc and technically problematic as well. One moral of the story is that the thesis that platonism affords a better account of the semantic appearances than nominalism, other things being equal, is not trivial. Another is that we should rethink our methodology in metaphysics.