Il giudice e l'esperto: deferenza epistemica e deferenza semantica nel processo

Experts in subjects other than law are taking on an increasingly important role in contemporary legal systems. Professionals specialized in all kinds of disciplines (e.g. physicians, engineers, chemists, town planners...) are often as indispensable as lawyers for the application of many legal provisions. How can judges rely on experts without allowing them to usurp their institutional role? Should the judge understand an expert opinion in order to be able to rely on it for the adjudication of a case? And if so, to which extent? Or is the judge allowed to rely on the expert’s authority accepting with deference the expert’s conclusions? This work attempts to address these questions introducing a conceptual distinction which has been traditionally overlooked in the relevant literature: the distinction between epistemic deference and semantic deference. “To rely on the expert’s authority” can mean two very different things: on the one hand, to make our commitment to the truth of a proposition conditional on the expert’s commitment (epistemic deference); on the other, to defer her also the determination of the propositional content we are committing to (semantic deference). While epistemic deference is an inherent feature of the physiological relation between judges and experts (every judge needs both lay and expert witnesses just as long as it is possible for her – after a general assessment of their credibility – to be deferential to them in the epistemic sense), semantic deference is not. When a judge is semantically deferent to the expert she loses control over the legal relevance of the fact-finding and is prone to commit serious mistakes in her legal reasoning, thus jeopardizing the epistemic integrity of the trial.