This paper discusses the legitimacy of general principles of private law as they have been formulated recently by the Court of Justice of the European Union and proposed by the European Commission. It addresses challenges from different strands in political theory including liberal perfectionism, political liberalism and Habermasian discourse theory. There are four specific lessons to be learned from these theories we have seen. First, the quest should not be for very general and abstract principles with a very broad scope, but rather for principles of an intermediate level of abstraction and a limited scope, which could explain and bring coherence to a set of rules, a legal doctrine, but not to the whole law of contract. Private law principles which are too general and sweeping would risk to neglect the need for internal diversification within private law. Secondly, these private law principles should be situated on the non-constitutional level of ordinary private law, subject to the constitution (including its horizontal effect) which in turn must be compatible, in order to be legitimate, with the political principles of justice that the EU polity has given itself. Thirdly, the CJEU, although an institution that is not in itself a less legitimate lawmaker than the legislator, also when it comes to private law principles, has a strong duty to explain itself and to provide good reasons for adopting general principles of civil law and for choosing certain principles, especially if these principles happen to be controversial, either from a comparative law point of view or along any of the other axes along which European citizens and European Member States may differ. Finally, there is no legitimate place for perfectionism in the deliberation on fundamental European private law principles; any private law perfectionism should be either local (in specific doctrines like unfair exploitation) or thin (limited to values like rationality). However, as long as we remain cautious is all these respects, the quest for general private law principles is perfectly legitimate. There is no contradiction in seeking to find general private law principles in a pluralist world.