Abstract

The role played by expert witnesses in legal adjudication has been at the centre of a lively debate over the past few years. This debate has focused on the reliability of expert opinions, their impact on fact-finding, and the relevance of scientific knowledge for legal adjudication in general. In this paper I argue that expert witnesses play a significant role not only in fact-finding but also in legal interpretation. More precisely, the use of expert opinions by judges may give rise to an interpretive problem that I call the "opacity of law." A legal norm becomes opaque if the judge can fix its reference on the basis of what some experts tell him, but he is not able to grasp the content of the norm he applies. When this occurs, expert witnesses determine the content of authoritative legal texts, giving rise to a number of interpretive problems. Here I analyse the source of this phenomenon, its peculiar characteristics and consequences, and the different sorts of opacity we can face in legal adjudication.