Book excerpt: On the History of the Idea of Law is the first book ever to trace the development of the philosophical theory of law from its first appearance in Plato's writings to today. Professor Letwin finds important and positive insights and tensions in the theories of Plato, Aristotle, Augustine, and Hobbes. She finds confusions and serious errors introduced by Cicero, Aquinas, Bentham, and Marx. She harnesses the insights of H. L. A. Hart and especially Michael Oakeshott to mount a devastating attack on the late twentieth-century theories of Ronald Dworkin, the Critical Legal Studies movement, and feminist jurisprudence. In all of this, Professor Letwin finds the rule of law to be the key to modern liberty and the standard of justice. This is the final work of the distinguished historian and theorist Shirley Robin Letwin, a major figure in the revival of Conservative thought and doctrine from 1960 onwards, who died in 1993.