In the case of the bonitary owner, the Praetor provided a defence to the vindicatio if there had been a transfer (improper or not).

If the immediate dis-possessor was not the owner, then both the bonitary owner and the good faith possessor would have a claim.

If res mancipi were transferred by traditio, full ownership would not pass and the recipient would become a bonitary owner.

The bonitary owner was protected against anyone, the good faith possessor was protected with regards to everyone except the owner.

Ultimately, Justinian abolished res mancipi, so the bonitary owner became owner and this theoretical problem was solved.

By giving the bonitary owner the protection of an owner, the Praetor had very much weakened the res mancipi distinction and come close to abolishing the need for mancipatio.

If either the bonitary owner or good faith possessor was dis-possessed, he could under the normal law claim a possessory interdict against his dis-possessor, but this did not cover further people if possession had been further transferred.

If however a bonitary owner kept the res in his possession for a certain amount of time (two years for land, one year for chattels) his title would become full title and he could assert himself as dominus.

The two cases where usucapio could be said to create two classes of people - the "bonitary owner" where formalities have not been complied with, and the "good faith possessor" where, for example, the seller is not the owner.

The Romans did not speak of the bonitary owner as dominus (as a normal owner would be), but rather to say that he had the thing in bonis from which the term "bonitary" is derived.