With respect to Article 1143 of the Act of 17 November 1964 – Code of Civil Procedure (Journal of Laws 2021.1805, consolidated text of 10 April 2021), the established opinion was that the court had full discretion as to how to determine the content of foreign law (and the practice of its application) which should be applied in the case. This was accepted in the literature and in the case law of ordinary courts and the Supreme Court. The methods expressly mentioned in the article were regarded only as possibilities that the court might but was not obliged to use.
This thesis remains valid also with respect to Article 51a of the Act of 27 Ju-ly 2001 – Law on the System of Ordinary Courts (Journal of Laws 2020.2072, consolidated text of 24 November 2020), which replaced Article 1143 of Code of Civil Procedure.
However, a key question arises whether and how the choice of the method used by court to determine the content of foreign law, and especially the prac-tice of its application, affects the procedural situation of the parties and the actual possibility of a higher court to review the findings in the course of the appeal procedure.
In the author’s opinion, the result of the proceedings may significantly depend on the method chosen by the court for determining the practice of applying foreign law. The widely accepted view that all available methods are equal does not mean that the effects of their application are also equal. Some met-hods of determining the content (and practice) of foreign law provide the parties with fuller protection of their rights, while others have a significant adverse effect on their procedural situation, making review of the judgment difficult. To eliminate these differences, it would be necessary to introduce a legal obligation for the court to inform about the content of foreign law, the established practice of its application, and the methods, data and sources used by court to determine them.