The article emphasizes the significance of EU studies for political thought and concepts. It deals with the seemingly technical topic of the membership of cabinet ministers in parliament. This practice arose in eighteenth-century Westminster and has been discussed since the mid-nineteenth century, Walter Bagehot's and Max Weber's writings being landmarks. When the European Parliamentary Assembly in 1960 interpreted the Treaty of Rome, it took the view, by a narrow margin, that membership of the Parliament was incompatible with membership of the Commission. The debate on the compatibility of dual membership could have been a way to promote the parliamentarization of the EU.