The postulate of a declining rate of has been a standard part of economics since the time of Adam Smith, and probably even before. Sometimes the reasoning behind the postulate is that of simple ceteris paribus-the law of varying proportions applied to investment. At other times it is deduced from a complicated dynamic model as in the theory of secular stagnation. The law has also been stated as an empirical fact. There have been theoretical doubts raised for example by Professor Hayek in his famous principle of investment that raises the demand for capital ,2 and more recently by Mr. Kaldor.3 Moreover, what available empirical evidence there is, does not suggest unqualified verification of the law. However, it is a fact that most of current economics includes some notion that the rate of profit tends to fall. Since the doctrine has loomed so large in the history of economics, and still plays a part in current theory-it is after all central to the framework of Keynes' General Theory-it is important to be acquainted with the origins and historical development of the law ; and it is with this latter point that Dr. Tucker is concerned. His book, a reprint of his Cambridge thesis, is an attempt to trace the development of theories of the effect of economic progress on the rate of profit (p. vii). The time-period considered is 1650 to 1850. In a book of this type there is always a problem of the method of presenting the material. Dr. Tucker sets out his material in strict chronological order. This is obviously in keeping with his attitude towards the study of the history of economics, if we are to judge this by his frontispiece quotation from William Ashley: a stream which may indeed change its size and direction, but has throughout a continuity of movement . We would normally expect a chronological approach to emphasise the continuity of thought rather than its discontinuities or revolutions . Whether an emphasis on continuity is beneficial to the understanding of the development of a social science seems to me to be arguable. Would, for example, the Keynesian system of thought have been absorbed more rapidly into accepted doctrine if Keynes had minimized its differences from the existing corpus of economic theory ? On the other hand, it can happen that excessive pre-occupation with chronology leads to an overemphasis on relatively minor disagreements missing thereby the 1 Progress and Profits in British Economic Thought 1650-1850, by G. S. L. Tucker. Cambridge University Press. 1960. 2 F. A. Hayek, Profits, Interest and Investment, ch. II. 3 N. Kaldor, Alternative Theories of Income Distribution , Review of Economic Studies, 1956.