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.