The subject of this book calls for some general observations on the nature and kind of what are called political ideas in the Middle Ages. Concerned as this book is with the sources, it is profitable to realize that political ideas in the Middle Ages had some peculiarities which are perhaps not at once obvious to people in the twentieth century. For politics and the study of political ideas now belong to a branch of scholarship which is autonomous and self-sufficient and which rests on its own laws, premisses and framework. It is as much an independent science as history, philosophy, theology, or, for that matter, law. Another point to be considered at the outset is the public at large. Today and for some time past the public that is engaged in framing, discussing and applying political ideas is to all intents and purposes identical with the electorate, and this in its turn comprises all men and women over a certain age. The presupposition for this is the dissemination of political ideas, whether by books, pamphlets, handbills, sound broadcasting, television, daily and weekly papers, quite apart from speeches by professional politicians. The literacy of, and response by, the public at large are indispensable. There is a virtually constant interchange between the mass media and the public, because the latter has a direct stake in both the major and minor questions of politics. The participation of the public—either directly or indirectly through their own representatives—in the decisions resulting in the law fosters this interchange of ideas and promotes mutual fructification.