Summary — An examination of the University lectures delivered by Bruno Leoni in Pavia suggests that it is fair to claim that Leoni had been studying the judicial thought of the Greek and Roman period in order to understand whether it was possible to single out a connection between the process by which Law comes about and the natural feeling of justice, which belongs to every individual and not just to the legislator. In this regard, Leoni captures meaningful elements by observing both the distinction made by the Greeks between nomos, physis and thesis (which Hayek developed later), and the Aristotelian theory of commutative equality (which is considered as the first attempt to study both law and economics) and, above all, the Roman " science of Law ", which aimed to discover the law rather than to produce it (an idea developed in Freedom and the Law).

After discovering Austrian marginalism Leoni realised the importance of comparing economic method with the study of law and politics. By reflecting on such a comparison and the idea of power, which Leoni considered as resources shared amongst all individuals, he achieved, by the end of the Fifties, some original definitions for the concepts of Law, Policy and State, which place him in a pivotal position within the politological studies of that period.

A few years later, through his portrayal of the process of Law-making, which starts with each individual and with the exchange of his own powers and claims with other individuals, Leoni reached his well-known theory of " Law as Individual Claim ". This implied a significant shift from the former predominant legal perspective — a shift that is comparable to the " marginalistic revolution " which took place in economic methodology. Moreover, according to Leoni, the starting point in the study of the Law should involve a weighing of the common individual claims as something that paves the way for Law. This theory may be considered a new philosophical vision of the social order, in which the idea of exchange lies at the heart of every single aspect of society, and which led Leoni to give a lesser role to the concept of coercion within society.