Participation of Unauthorised Persons in Issuance of Decisions in Civil Proceedings - Remarks on the Basis D. 1,14,3 and D. 41,3,44 pr.SummaryAccording to Polish civil procedure a sentence given by an unauthorized person is invalid. This was not always the case in ancien Roman law. Ulpianus declared that when a slave, who escaped from his master, became a praetor, his acts were valid. He took into consideration serious problems of those who had put their trust in the praetor’s office as well as the respect for humanitas. A basic common sense requires that what was well decided, should be considered valid. According to the author, Ulpianus realized that the rule of ius civile which determined the requirements for entering in a praetor’s duties had the character of a guarantee. If the purpose, for which this rule was established, was achieved, such acts should be accepted as valid.The question arises whether that approach could be applied to contemporary cases of iudex incompetens. Furthermore, whether it would be justifiable to extend this solution to other - not only procedural – but also material, guarantee rules?The answer is not easy. In D. 41,3,44 pr., a pater familias conducted the procedure of adrogation (adoption) improperly. Papinianus decided that, although pater familias made a justifiable mistake, all that the son enacted in the name of the father, was invalid. Nevertheless a different rule, as the jurist says in D. 41,3,44 pr., must be observed in the case of homo liber bona fide serviens - a person, who being unaware of his free man status, served as a slave. Actions taken by such a person were valid (the purchaser of a slave had to be protected), since transactions of that kind happened very often. More importantly, any other solution would be against the public interest. O n the other hand, it was very rare for a pater familias to wrongly adrogate, therefore the example of pater familias did not create a general rule.It seems quite difficult to indicate one principle which could be applied to all the guarantee rules. As far as the case of an unauthorized person giving sentence is concerned, the Roman private law shows that the regard for the public interest may sometimes justify solutions different from those preferred by Polish law.