Decisions of the Belgian ordinary courts and judgments of the Belgian Court of Cassation have a retroactive effect. This is only logical: the legal facts at the basis of the dispute originated in any case prior to this judgment. Consequently, the retroactive effect constitutes the very essence of the judgment, i.e. the settlement of the dispute.
Sometimes reference is made to the declaratory effect of judgments which is based on the passive role of judges. The declaratory effect implies that judges do not create law; according to this theory they merely discover existing law of which the judgment is proof. Within this line of reasoning, the judicial decision-making process is reduced to a syllogistic reasoning: with the major premise in the statute, and the facts of the case as the minor premise, the conclusion is derived ‘automatically’.
This declaratory theory has long since been superseded and the more active role of judges is widely accepted. A simple syllogistic argument is not feasible; application entails interpretation and with this, judges often create law. The fact that the Belgian legislator also prohibits a denial of justice when the law is silent, unclear or incomplete only enhances the law-creating role of judges.
It becomes clear that given this active role of the judge, the retroactive effect of his decisions may create significant uncertainty. After all, because of the effect ex tunc, a judicial decision is applied on to a past even as though it was the law at the time of that event. Consequently, when the judge imposes a new rule and/or deviates from established case law, parties are confronted with the application of a new rule which they could not have predicted at the time of the past event. This is why the temporal effect of a judicial decision needs to receive due attention.
Since 2002, the annual report of the Belgian Court of Cassation has explicitly confirmed the law-creating role of this Court. (s.n. – M.M.-B.)
(The Interplay of Temporal Effects of Judicial Decisions within the Belgian Legal Order în The Effect of Judicial Decisions in Time, Intersentia, 2014, la pp. 44-5)