THE PRESENT STUDY proposes to explore the history of the problem of 'reason of state' in a constitutional political order. The writers treated belong among the 'great' in modern political thought and therefore it is not and cannot be a question of dealing with the integral thought of the writers here examined. All we can hope to do is to seek out those aspects which bear more immediately upon this particular problem. Ratio status,-the very term shows that we are moving within the context of the great tradition of Western rationalism, where everything has its particular ratio or inner rationale which it behoves the mind to grasp and to understand. For the idea of such rationes is prominent in the Middle Ages,-an aspect of the matter which receives scant attention in Friedrich Meinecke's magistral treatment of the subject Die Idee der Staatsr?son in der Neueren Geschichte published in 1925 and by now become something of a classic. Perhaps partly because of his lack of sympathy for this rational basis of the idea which he was discussing, he also paid scant attention to that aspect of it which we are particularly concerned with here: reason of state in its application to the government of law, the constitutional order, in short 'constitutional reason of state' or more precisely 'reason of the constitutional state.'