We take 'natural' as a title that is provided by nature, as in 'the owner of an assertion'.
For futher details, see ownership.
The ability to distinguish between (non)owners of an entity enables one to identify the party and the duties (and rights) it has regarding the owned. One may want to do so either to establish whether or not the owned entity, e.g. if it is an actor, can be trusted to behave according to its owner's policies. Or, one may want to do this in order to settle a dispute it has.