Law and Politics in Constitutional Democracy. On Principia iuris - The article deals with the relationship between politics and law in the constitutional democracy theory put forward by Luigi Ferrajoli, moving from the analysis of the typology of powers developed in Principia iuris. In particular, the author reflects on the nature of legislative power, in some instances qualified by Ferrajoli as « autonomous » power, more often conceived as « discretionary » power, whose aims are thought to be to a large extent pre-determined by the constitution. If such a conception may lead one to think of a subordination of politics to law, and even to a reduction of politics to a mere implementation of constitutional law, a thorough reading of Ferrajoli’s work leads to a more articulated and problematic judgement. On Principia iuris.