As summarized by Sandrine Baume in her recent book on Kelsen, "In 1927 recognized his debt to Kantianism on this methodological point that determined much of his pure theory of law: 'Purity of method, indispensable to legal science, did not seem to me to be guaranteed by any philosopher as sharply as by Kant with his contrast between Is and Ought. Thus for me, Kantian philosophy was from the very outset the light that guided me.'" Kelsen's high praise of Kant in the absence of any specific neo-Kantians is matched among more recent scholars by John Rawls of Harvard University. Both Kelsen and Rawls also have made strong endorsements of Kant's books on "" (1795) and "Idea for a Universal History" (1784). In his book titled "What is Justice?", Kelsen indicated his position concerning social justice stating, "[Suppose that it is possible to prove that the economic situation of a people can be improved so essentially by so-called planned economy that social security is guaranteed to everybody in an equal measure; but that such an organization is possible only if all individual freedom is abolished. The answer to the question whether planned economy is preferable to free economy depends on our decision between the values of individual freedom and social security. Hence, to the question of whether individual freedom is a higher value than social security or vice versa, only a subjective answer is possible,"