A real right vests in a person with respect to property, inherent in his relation to it, and is good against the world (erga omnes).
The primary real right is ownership (dominium) (freehold, leasehold, commonhold).
Whether possession (possessio) is recognized as a real right, or merely as a source of certain powers and actions, depends on the legal system at hand.
In Latin grammar the action against the thing demands a fourth case.
By mistake the common law terminology now uses the fourth case for describing the right itself.