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.
Philosophy of Physical Magnitudes
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