EN
The aim of the article is to explain the Roman roots of one of the forms of a deduction, i.e. a compulsory deduction, which is normalized in the Polish legal system by articles 498-505 of the civil code. Basing his analysis on the origins of Roman law and the subject literature, the author establishes the substantive and legal reasons for a deduction (subjective and objective ones). He explains the character of changes introduced to this institution by the law of Justinian. He solves the problem of the admissibility of compensation 'ipso iure', introduced in the Justinian's constitution of 531. The article enables to draw a conclusion that there is a correlation between the deduction requirement in the Polish civil law.