“Secondo natura” e “contro natura”: natura e legge nel libro I della Repubblica di Platone

Trasymachus‟ position on justice in Plato‟s Republic Book I is a classical quaestio. The paper highlights the differences between the notions of justice and law. Many scholars assume that Trasymachus produces at least two dif-ferent definitions of justice. The paper shows how Trasymachus‟ position is unitary and coherent and how the assumption of the two definitions depends on the fact that those scholars consider justice and law to be the same, which is not so. Trasymachus adopts a point of view based on the ontology and on an anthropology typical of a non-philosopher, while Plato constructs his position on justice according to his assumptions on the relation between the forms, physis and human soul; this means that Trasymachus‟ position is “against nature”.