 When we turn from classical mechanics to relativity theory and quantum theory, the a posteriori case against conceiving physical quantities as intrinsic is even stronger. Consider mass and charge, most metaphysicians’ favourite and commonly relied upon examples of intrinsic properties of a piece of matter (in particular a point particle). In relativity theory, mass is identified with energy (“mass-energy”). In a relativistic field theory, such as Maxwell’s theory of electromagnetism, the all-pervading electromagnetic field has mass-energy. It also has momentum, stress and other traditionally mechanical properties. So mass is no longer conceived as an intrinsic property of localized lumps of stuff, let alone of point particles. Furthermore, the attribution of mass, momentum, stress, etc., to the electromagnetic field, or to a matter field such as a continuous fluid, depends upon the metrical structure of spacetime. So these quantities are not intrinsic, but, rather, relational properties. They are properties that the radiation or matter field in question has in virtue of its relation to spacetime structure (Lehmkuhl 2011).