Political theory and political philosophy (used interchangeably in this article) have always played a role in public life. The argument pursued here is that this is not accidental. We cannot understand in an explanatory sense developments in public policy without understanding the structure of ideas that influence those developments, including the normative presuppositions at the core of those structures of ideas. However, we can pass from explanation in the narrow sense to justification and the evaluation of the merits of those ideas. The techniques of normative political theory are invaluable in this context of justification and evaluation. Two examples are given to illustrate this last claim.