What is Fundamental in Special Relativity?

Balashov and Janssen (2003) on the one hand and Brown and Pooley (2006) on the other hand debate whether the structure of Minkowski spacetime or the Lorentz invariance of physical laws fundamentally grounds Special Relativity. In addition to a debate about what is fundamental, it is a debate about whether the Minkowskian structure of spacetime explains the Lorentz invariance of physical laws or the Lorentz invariance of physical laws explains why spacetime is Minkowskian. I argue neither side states what fundamentally grounds Special Relativity. Instead, a constructive derivation of Special Relativity is provided based on the properties of light and a homogeneous, isotropic universe. Special Relativity is shown to be concerned with nothing more than the units of space and time and the effect of relative motion on those units as described by the Lorentz boost. Minkowski spacetime can be constructed from the Lorentz boost, but it does not add structure to spacetime. Dynamical laws governing the microstructure of matter in turn instantiate Lorentz boosts because they incorporate units of space and time in their equations.