SUMMARYAccording to the neo‐classical theory of economic growth, the rate of growth of output tends towards a value which is independent of the proportion of the national income saved. If the proportion of saving changes, the rate of economic growth reaches—after an adjustment process—its original level, which (with a constant labour force) is alone determined by technical progress and the elasticity of the output in respects to changes in the use of the factor capital. Amongst the infinity of possible proportions of investment there must be one, which leads to a maximazition of consumption. It can be shown, that consumption is maximized, if the proportion of investment equals the elasticity of the output to the factor capital.The theorem that the rate of economic growth is independent of the proportion of investment is only valid, if technical progress is autonomous. The equilibrium system postulated in this theorem is indeterminate to the extent that technical change is induced by the process of capital formation. Under these conditions saving and investment decisions again become the determining parameters of the growth rate. Now technical progress may be partly independent of capital formation, but this does not mean that it is totally autonomous. It would be more correct to say that it is a function of, for example the level of technical knowledge and expenditure on education, even if these factors do not enter the analysis explicitly as factors of production. The neo‐classical theory of equilibrium, however, is based on the assumption that technical progress is simply a function of time; thus this theory of equilibrium is based upon the choice an inappropriate underlying production function.Moreover, only the rate of economic growth is dependent upon investment activity but not the level of output. With an increasing proportion of investment the level of output increases, tending to a new equilibrium path.There exists a determinable proportion of investment which leads to a maxi‐mazition of consumption. Pearce has shown recently, that this is valid only under the condition, that several economies which are on the equilibrium path of growth, are compared. If the optimum path is left temporarily (through an increase in the proportion of investment), a (temporary) increase of consumption, which exceeds the consumption foregone, is obtained. Beyond it, it can be shown, that the optimal proportion of investment must be higher, the more technical progress is induced. If technical progress is not autonomus, the system is again open: in the long run the greater the accumulation of capital the greater the possible consumption level. It is the subsistence minimum which determines the proportion of investment.