Supreme Court Justice: the doctrine of the prohibition of contradictory conduct is a wild card, not a samurai sword

The doctrine prohibiting contradictory conduct applies when there is a defect in a legal relationship and a decision based on general rules would be manifestly unjust. Where such rules are in effect, a reference to them is superfluous.

This was emphasized by Judge Vasyl Krat of the Civil Cassation Court of the Supreme Court during the webinar «The legal doctrine of venire contra factum proprium (prohibition of contradictory conduct)». The event took place on October 15, 2026, at the initiative of the UNBA NextGen in the Odesa region. The meeting was moderated by the Committee’s regional representative Viktoria Pinchuk.

According to the judge, the doctrine is not explicitly mentioned in the Civil Code: it is a manifestation of the principle of good faith. The sole legal basis for its application is paragraph 6 of Part 1 of Article 3 of the Civil Code. This is a discretionary concept that does not operate independently or universally with respect to all possible disputes.

V. Krat recalled the situation that marked the beginning of the doctrine’s application in the Supreme Court’s practice. A landlord had been receiving rent for the use of a land plot but later, citing an expert opinion, claimed that he had not signed the lease agreement. It is precisely this defect that allows for the application of the doctrine, as otherwise the decision would be manifestly unjust.

The judge cautioned against filing cassation appeals that rely on the doctrine of the prohibition of contradictory conduct when the essence of the case lies elsewhere. «It is not a universal samurai sword to be invoked in every case», - he noted. Responding to a question about credit disputes, insurance, and suretyship, the speaker explained: if there is no specific defect, the doctrine is unnecessary, since the provisions governing credit agreements, performance of obligations, mistake, or termination of a contract apply.

The doctrine of the prohibition of contradictory conduct is a substantive legal construct and therefore applies only to civil relations as defined in Part 1 of Article 1 of the Civil Code. Consequently, as explained by V. Krat, it does not extend to relations in enforcement proceedings or to administrative litigation. Nor should it be equated with estoppel — an institution of Anglo-Saxon law: these are concepts belonging to different legal systems. A separate principle applies in litigation — procedural good faith, specifically Article 44 of the Code of Civil Procedure, with its own specific meaning—and thus the doctrine of the prohibition of contradictory conduct does not apply to procedural relationships.

The speaker emphasized that the doctrine of the prohibition of contradictory conduct blocks, rather than nullifies. It prevents a transaction from being declared invalid or a contract from being deemed not to have been concluded, but it does not constitute grounds for challenging it. Another possible consequence is the termination of the right to contest. As an example, the judge cited a case in which a person renounced an inheritance in writing after the deadline for accepting it had expired and subsequently failed to exercise their right to contest for a long time. Although such a statement had no legal consequences, the court considered it a manifestation of conduct.

Therefore, when the person’s heirs attempted to exercise the right to contest the inheritance after the person’s death, the court concluded that the right had been extinguished.

When asked whether a court may apply the doctrine of the prohibition of contradictory conduct if the parties do not invoke it, V. Krat answered in the affirmative. Like the manifestation of the principle of good faith, the doctrine of the prohibition of contradictory conduct does not require a party’s assertion, unlike, for example, the statute of limitations.

«The Court of Cassation has repeatedly emphasized that when there are certain defects and the decision would be manifestly unjust, the doctrine of the prohibition of contradictory conduct should be applied as a «wild card», - V. Krat concluded.