http://webs.morningside.edu/slaven/Physics/relativity/relativity3.html Dave Slaven: "Einstein's first postulate is that the physical laws of nature are the same in all inertial reference frames. His second postulate is simply a consequence of applying this principle to the laws of electricity and magnetism. That is, if Maxwell's equations are taken as laws of nature, then they (and all their consequences) must hold in all inertial frames. One of the results of this is Einstein's second postulate: The speed of light is the same in every inertial frame of reference. Einstein's first postulate seems perfectly reasonable. And his second postulate follows very reasonably from his first. How strange that the consequences will seem so unreasonable."