For Better and for Worse. Abstractionism, Good Company, and Pluralism

A thriving literature has developed over logical and mathematical plural- ism - i.e. the views that several rival logical and mathematical theories can be equally correct. These have unfortunately grown separate; in- stead, they both could gain a great deal by a closer interaction. Our aim is then to present some novel forms of abstractionist mathematical pluralism which can be modeled on parallel ways of substantiating logi- cal pluralism (also in connection with logical anti-exceptionalism). To do this, we start by discussing the Good Company Problem for neo-logicists recently raised by Paolo Mancosu (2016), concerning the existence of rival abstractive definitions of cardinal number which are nonetheless equally able to reconstruct Peano Arithmetic. We survey Mancosu's envisaged possible replies to this predicament, and suggest as a further path the adoption of some form of mathematical pluralism concerning abstraction principles. We then explore three possible ways of substantiating such plu- ralism - Conceptual Pluralism, Domain Pluralism, Pluralism about Crite- ria - showing how each of them can be related to analogous proposals in the philosophy of logic. We conclude by considering advantages, concerns and theoretical ramifications for these varieties of mathematical pluralism.