I was wondering whether, making a comparison between the propagation of electric current through a conductor and the propagation of an electromagnetic wave through a dielectric, one could establish the following correspondences: Ability of a material to facilitate the propagation of the “influence”: - If the influence is the electric current and the material is a conductor, that is its CONDUCTIVITY. - If the influence is an EM wave and the material is a dielectric (that is to say, an EM CONDUCTOR), that is its PERMITTIVITY, which could thus be labelled as EM CONDUCTIVITY. Ability of a specific sample of the material in question to propagate the “influence”: - If we talk about an electric current and a conductor, that is… CONDUCTANCE? Does this concept exist at all? - If we speak about an EM wave travelling through a dielectric, that is its CAPACITANCE, which could also be labelled as… EM CONDUCTANCE. I had this is mind and the PF’s entry on permittivity gave me a sort of confirmation. Certainly, the terms permittivity and capacitance may be more revealing in other contexts. But, if the context of the discussion is propagation of the EM wave, I would like to know if this is a correct didactic approach: whether one could say, “well, it will propagate better or worse depending on the EM conductivity of the material and the EM conductance of the object in question (based on its geometric characteristics), which is what you call, respectively, permittivity and capacitance”.