One cannot determine whether a book is a work of political philosophy merely by glancing at its contents. Heidegger's Being and Time is a case in point. It offers no discussion of the topics which are commonly thought to constitute political philosophy—the state, the nature of law, human rights, and so on. But particular themes such as these reflect in large part the actual conditions which prevailed at certain times and places, fourth-century Athens and seventeenth-century England, for example, so they must not be thought to constitute an outline of the eternal problems of political philosophy. When a philosopher embarks upon a new line of thought at a different time and under novel circumstances, he may find himself instituting a new vocabulary for the problems of the human community.