The Age of Political Arithmetic Minoru KAWAKITA Political Arithmetic was invented by John Graunt, and popularized by William Petty in Seventeenth-Century England. It has been, so far, interpreted as one of the origins of the modern economics. Historians wanted to look for Adam Smith's forefathers among the political arithmeticians. In this essay, I will try to re-evaluate the political arithmetic in the intellectual milieu of early modern history of Europe. Graunt, Petty, Gregory King and others lived in the real world of the seventeenth century. They were not exclusively interested in the abstract theory. They could not foresee Adam Smith at all. As realistic observers of the contemporary society and nation, they could find a new idea of history, idea of sustained growth which became a backbone of the Modern World-System. The political arithmeticians were mainly interested in the comparative strength of the nascent British nation, in comparison with the Netherlands and France. In making such comparisons, they put a stress on the demography. Number of people was the most important factor of the national strength for them. They were keen, therefore, to trace the history of population and to foresee the future number of the people. In doing so, they adopted an idea of sustained growth. Marx found the essence of modern capitalism in the incessant accumulation of capital and W. W. Rostow asserted the self-sustained economic growth. But the concept of sustained growth itself was invented by the Seventeenth-Century political arithmeticians.