As Louis MacNiece wrote, “World is crazier and more of it than we think, Incorrigbly plural.” Evidently, then, we need a plural logic! Or so say quite a few. And enough has been written on the topic for it to be time to pause to take stock.
I have just now started reading Salvatore Florio and Øystein Linnebo’s The One and The Many: A Philosophical Study of Plural Logic, newly published by OUP with an open access arrangement which means that a PDF is free to download here. The book aims to take stock and explore the broader significance of plural logic for philosophy, logic, and linguistics. What can plural logic do for us? Are the bold claims made on its behalf correct?
I’ll say straight away that Florio and Linnebo write very lucidly in an attractively readable style. Though it is not entirely clear, perhaps, who the intended reader is. The opening pages seem addressed to a pretty naive reader who e.g. may not even have heard of Cantor’s Theorem (p. 3); yet pretty soon the reader is presumed e.g. to understand talk of defining logical notions in terms of isomorphism invariance (p. 22). Again, if the reader really was new to the topic and had never seen before one of the now standard core logical languages for plural logic and its associated core deductive system, the initial brisk outline presentation (pp. 15-20) might perhaps be rather too brisk. But I’ll try not to nag you much about this sort of thing. Whatever F&L’s intentions, I’ll take the likely actual reader of their book to be someone who has some logical background and in particular has a modicum of prior acquaintance with plural logic and some of the debates about it; and then their brisk early remarks can serve perfectly well as reminders getting us back the swing of thinking about the topic.
So let’s dive in. In the short Chapter 1, ‘Introduction’, F&L highlight three questions which are going to run through their discussion:
- Should the plural resources of English and other natural languages be taken at face value or be eliminated in favor of the singular?
- What is the relation between the plural and the singular? When do many objects correspond to a single, complex “one” and what light does such a correspondence shed on the complex “ones”?
- What are the philosophical and other consequences of taking plurals at face value?
Not, I think, that we are supposed to take these as sharply determinate questions at this stage: take them as pointers to clusters of issues for discussion. F&L also give early spoilers, indicating some lines they are going to take.
In response to (1) they announce they are pluralists, resisting the wholesale elimination of plurals (while, they say, wanting to resist some of the usual arguments against singularism). On (2) they say — surely rightly — that the question is going to entangle us tricky issues in metaphysics, semantics, and the philosophy of mathematics. We can’t, as it were, argue for a particular line on plural logic in isolation; rather we going to have to “chose between various “package deals” that include not only a plural logic but also commitments far beyond”. On (3) F&L trail their view that many of the claims that have been made for plural logic — such as that it “helps us eschew problematic ontological commitments, thus greatly aiding metaphysics and the philosophy of mathematics” — are, in their words, severely exaggerated. Leaving aside the ‘severely’, I’ll probably find myself endorsing a verdict that some of the claims that have been made for plural logic are somewhat overblown. But I’ll be interested to see to see how the detailed arguments pan out.
To be continued.