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*arbitrary*way (in the sense of, not physically forced, even if convenient) to coordinatize time, and hence the Lorentz transformation is an

*arbitrary*mapping between the coordinates of different reference frames, versus saying that the Einstein convention is

*fundamental*to what we mean by time, and the Lorentz transformation is

*fundamental*to what we mean by motion. I am rather of the former school, that what is physically fundamental is a deeper symmetry that allows the Einstein convention to be a particularly convenient coordinate choice, but that its physical significance comes entirely from how it simplifies the coordinatizations when we apply the laws of physics. But others might argue that the simplification is so fundamental that it would be foolish for us to imagine that "reality itself" could be doing anything different, even if just a means for recognizing equivalent possibilities.

Note, in particular, that the isotropic and constant speed of light in an inertial frame is a ramification of Einstein's coordinatization prescription, so an equivalent way to ask this is, is the isotropic speed of light a law of nature or just the proof that there exists a particularly elegant coordinate possibility? As the former is often taken as a

*postulate*of special relativity, are we messing up the proper axiomatic structure of our art here?