Tính ổn định của trạng thái cân bằng ngắn hạn yêu cầu tham số được chọn như vậy mà các mẫu số (và do đó số nhân ngắn hạn) là tích cực. Kể từ khi sản lượng và tiêu thụ không thể được tiêu cực, biểu hiện trong (15) cũng đòi hỏi một tử số không âm, có nghĩa là, các đặc điểm kỹ thuật tuyến tính của chức năng tiết kiệm chỉ được áp dụng trong một loạt các giá trị đáp ứng hạn chế tiêu cực không. 5 Harrod chắc chắn sẽ có suy nghĩ như vậy | J. SMITHIN Second the aggregate demand function is assumed to be less sensitive to the interest rate than is aggregate supply and hence the AD schedule cuts the AS from above. The relative insensitivity of aggregate demand to interest rate changes was of course a staple of the Old Keynesian literature and was implicit in the Keynesian Cross . However in that context it was not combined with a palpable degree of interest sensitivity of supply as is done here. For simplicity the AD schedule in Fig. is shown as completely interest insensitive. However clearly nothing would be changed by allowing some interest elasticity as long as this is less than on the supply side. The third important point is that in Fig. the real rate of interest is taken to be a financial variable determined essentially by the monetary policy of the central bank. It is determined outside the aggregate demand and supply nexus itself and in the diagram shows up as a horizontal line across the page at a predetermined level r . The underlying monetary theory is therefore that of the Post Keynesian horizontalist school in which the interest rate including the real rate is effectively a policy instrument and the money supply is endogenous. This is contrasted with Barro s version in Fig. in which there in no theory of money and the interest rate is taken literally to be a real non-monetary variable. Victoria Chick . 1984 1986 1991 1995 has written extensively on Post Keynesian monetary theory endogenous money the theory of banking and alternative views on interest rate determination. She has indeed described hori-zontalism . that of Moore 1979 4 as an extreme position Chick 1986 116 while nonetheless making it clear that as a first approximation this is still a far more reasonable assumption than the alternative neoclassical extreme. The main objection to treating the interest rate as a purely policy-determined variable would be the extent to which this neglects Keynes s insights .
