Theories of capital have historically been amongst the most fertile sources of economic controversy. Many aspects of the modern debate, if not the techniques employed in its exposition, would have been as familiar to Marx, Ricardo, Bohm-Bawerk or Wicksell as to any present-day Cambridge economist. That conotroversies should arise in the course of theorizing cm the concept of capital and the function of profit is not surprising: that these debates have been so vigorous and virluent cannot be divorced from the general ideological and specific implications associated with the theories. In the context of a textbook on the theories of economic growth, the central question associated with capital that must he faced is whether the existence in the real world of heterogeneous capital goods inevitably invalidate; the conclusions of simple theories of "parables" which incorporate no more than a conception of a single, malleable, capital good. All the Cambridge writers have, to a greater or lesser extent, been concerned to deny that any unit can be found in which heterogeneous capital goods can be aggregated so as to simultaneously satisfy the pair of neoclassical requirements described above. Some of them have been more prepared than others to countenance such a possibility or, for practical purposes, to use some concept of aggregate capital in their models, but they are all deeply suspicious of attempts to use aggregate production function, incorporating aggregate "capital", so as to explain the flow of output, relative factor prices and the distribution of income.tribution of income.