What Peter didn't know. Reflections on spatial size

Abstract

The person of the initial thought experiment knows all non-indexical physical facts about things of the external world but not their real size. This highlights a tension between two rather uncontroversial views about spatial objects: (1) the particular size of such objects is non-conceptual; (2) truths about a quantity like size are relational. The problem is that relational truths about size are conceptual. And in order to distinguish particular from conceptual size, one seemingly needs a measure of 'worlds'. I argue that in the role as embodied agent, man may supply such a measure. This is also taken as an argument for Kantian transcendental idealism and empirical realism.