  The consideration of certain examples lends plausibility to the idea, prevalent in the literature, that the bridge laws should be considered to express some kind of identity relation. For instance, Sklar notes that the reduction of the “theory” of physical optics to the theory of electromagnetic radiation proceeds by identifying one class of entities — light waves — with (part of) another class — electromagnetic radiation. He says “… the place of correlatory laws [bridge laws] is taken by empirically established identifications of two classes of entities. Light waves are not correlated with electromagnetic waves, for they are electromagnetic waves.” (Sklar 1967, 120) In fact, if something like Nagelian reduction is going to work, it is generally accepted that the bridge laws should reflect the existence of some kind of synthetic identity.