Philosophers oftenoperate with amisleading caricature ofscientific statements in terms ofpropositions from first-order logic with primitive, qualitative predi-cates, such as ‘For all x, ifRx then Bx’, where R and B are to be understood as, for example, ‘being a raven’ and ‘being black’, respectively. The much richer properties that are in fact central to sciences such as physics, chemis-try and biology are physical magnitudes represented by numerical quantities –forexample spatial length, temporal duration, electric charge andmass –and/or relations between these magnitudes. When planets and molecules ‘have mass’ or ‘are spatially separated’, they instantiate these determinables in virtue of instantiating determinate physical magnitudes ordeterminate magnitude ratios,each with a rich quantitative structure. 1 For example, that the Earth and Mars are massive is true in virtue ofthem standing in a determinate mass relation-ship, namely a ratio of1:0.107. A common claim is that an electron is charged because it has a determinate electric charge that we refer to as 1.6 · 10 −19 Cou-lomb. Moreover, most of these physical magnitudes are dimensional: that is,their representation in terms ofnumerical quantities depends on a conventional unit. For instance, until recently the masses ofobjects were expressed in terms oftheir relationship to an arbitrarily chosen object, stored in Paris, that served as the standard unit ofmass.