All behavior of physical systems is independent of which inertial system is the reference frame for describing the behavior. Since there is no reason to prefer one, neither is preferred. Given one inertial frame, any other reference frame whose origin moves along a straight line at constant speed and which is non-rotating relative to the inertial frame, is itself an inertial frame. All inertial frames are non-rotating and have uniform motions relative to one another. One inertial frame has uniform velocity relative to any other inertial frame.
All physical behavior is explainable by physical laws of change.
All physical behavior conforms to physical laws of motion. All physical behavior resulting from objective procedures conforms to physical laws of motion.