Emancipatio

"EMANCIPA′TIO was an act by which the patria potestas was dissolved in the lifetime of the parent, and it was so called because it was in the form of a sale (mancipatio). By the Twelve Tables it was necessary that a son should be sold three times in order to be released from the paternal power, or to be sui juris. In the case of daughters and grandchildren, one sale was sufficient." Article by George Long, M.A., Fellow of Trinity College on pp455‑456 of William Smith, D.C.L., LL.D.:

See call no man Father

"The patria potestas could not be dissolved immediately by manumissio, because the patria potestas must be viewed as an imperium, and not as a right of property like the power of a master over his slave. Now it was a fundamental principle that the patria potestas was extinguished by exercising once or thrice (as the case might be) the right which the pater familias possessed of selling or rather pledging his child. Conformably to this fundamental principle, the release of a child from the patria potestas was clothed with the form of a mancipatio, effected once or three times. The patria potestas was indeed dissolved, though the child was not yet free, but came into the condition of a nexus. Consequently a manumissio was necessarily connected with the mancipatio, in order that the proper object of the emancipatio might be attained. This manumissio must take place once or thrice, according to circumstances. In the case when the manumissio was not followed by a return into the patria potestas, the manumissio was attended with important consequences to the manumissor, which consequences ought to apply to the emancipating party. Accordingly, it was necessary to provide that the decisive manumission should be made by the emancipating party; and for that reason a remancipatio, which preceded the final manumissio, was a part of the form of emancipatio." (Unterholzner, Zeitschrift, vol. II p139; Von den formen der Manumissio per Vindictam und der Emancipatio).