Full Idea
Fifty years ago, Quine convinced everyone who cared that the argument for abstract objects, if there were going to be one, would have to be a posteriori in nature; an argument that numbers, for example, are indispensable entities for 'total science'.
Gist of Idea
Quine's indispensability argument said arguments for abstracta were a posteriori
Source
report of Willard Quine (On What There Is [1948], §1) by Stephen Yablo - Apriority and Existence
Book Reference
'New Essays on the A Priori', ed/tr. Boghossian,P /Peacocke,C [OUP 2000], p.196
A Reaction
This sets the scene for the modern debate on the a priori. The claim that abstractions are indispensable for a factual account of the physical world strikes me as highly implausible.