A great deal of literature on the status and meaning of the Laws of Inertia in spacetime theories has nurtured and given wide currency to the claim that the laws are conventional in character, that they are definitions, or circular and without empirical content.
Philosophers who argue for the conventional character of the laws, do so, either emphasizing epistemological or ontological considerations concerning the structure of spacetime.
Those who argue for their conventional character mainly on epistemic grounds, point out, that the laws do not supply independent criteria of what is to count as force-free or natural motion. The only way of knowing when no forces act on a body is that it moves as a free particle traveling along the geodesies of spacetime. But how, without already knowing the geodetic structure of spacetime is one to determine which particles are free and which are not?