This paper focuses on the practice of making reference to foreign law in legal adjudication. On the one hand, this practice has received overwhelming attention from legal scholars in the last two decades under the headings of “judicial dialogue”, “judicial cross-fertilization” or “constitutional conversation”; on the other hand, a systematic, theoretical picture of this practice is still lacking. The paper aims to bridge this gap by elucidating the structure of legal comparison in judicial decision-making from the point of view of argumentation theory. To this end, the paper examines the various forms of comparative reasoning, identifies the set of their implicit premises and shows under what conditions referring to foreign law in legal adjudication is justified on its own grounds. This analysis will lead us to discuss the thesis according to which comparative reasoning by courts is changing the nature of law and the structure of contemporary legal systems.
