Pure Theory of Law () is a book by legal theorist Hans Kelsen, first published in 1934 and in a greatly expanded "second edition" (effectively a new book) in 1960. The second edition appeared in English translation in 1967, as Pure Theory of Law, the first edition in English translation in 1992, as Introduction to the Problems of Legal Theory. The theory proposed in this book has probably been the most influential theory of law produced during the 20th century. It is, at the least, one of the high points of modernist legal theory. Editions The two editions of Kelsen's book were separated by twenty-six years, and the second edition (1960) was almost twice the length of the first in the detail of its presentation. The original terminology which was introduced in the first edition was already present in many of Kelsen's writings from the 1920s, and were also subject to discussion in the critical press of that decade as well, before it was first published in 1934. Although the second edition was significantly longer, the two editions had a great deal of similarity of content, and much of the material covered in the volumes is consistent not only with one another, but also with many of Kelsen's previous writings from the 1910s and 1920s. The following sections herein shall follow Kelsen's own preference for the presentation of his main topics of the pure theory of law as he presented them in the second edition of this book. Chapters I. Law and Nature In the first paragraph of Pure Theory of Law, Kelsen introduces his theory as being a theory of positive law. This theory of positive law is then presented by Kelsen as forming a hierarchy of laws which start from a basic norm (Grundnorm) where all other norms are related to each other by either being inferior norms, when the one is compared to the other, or superior norms. The interaction of these norms is then further subject to representation as a static theory of law (Kelsen's chapter 4) or as a dynamic theory of law (Kelsen's chapter 5). II. Law and Morals Kelsen's strict separation of law and morality, in Chapter Two of Pure Theory of Law, was an integral part of his presentation of the Pure Theory of Law. The application of the law, in order to be protected from moral influence or political influence, needed