The Two Kinds of Adoption
There were two kinds of adoption:
(1) The adoption of a person sui juris, which resulted in bringing under the potestas of the adopter a person previously not under power. This was called arrogation. This was the older form, and originally only persons sui juris could be adopted.
(2) The adoption of a person alieni juris, which resulted simply in the transfer of the person adopted from one potestas to another. This was called simply adoption.