这无害于存在

JMK arguing towards the General Theory
The emergence of effect demand

1931年至32年，John Maynard Keynes (JMK)考虑的问题是：Treatise of Money (TM)仅给出了造成了不均衡的初始原因，却无法解释调整过程。在不同的TM分析区间，价格如何变化？产出和价格如何从一个均衡过渡到另一个均衡？在思索的过程中，分析框架逐渐从投资、储蓄分析转向花费(disbursement)、收入(earning)分析，也就后来成为通论主题的有效需求分析。
ΔQ=ΔI-ΔS=ΔI-Δ(E-F)= ΔI+ΔF-ΔE=ΔD-ΔE，其中Q表示利润，I、S、E、F、D分别为投资、储蓄、总收入、消费以及总花费。

在这段时间内，后来被称为乘数效应(multiplier effect)的思想也隐约现诸笔端：当期企业家利润的降低，会延迟投资决策，不仅企业家自己的支出(expenditure)下降了，其他消费者的支出也会下降——也就是说，初始花费(disbursement)的下降，会导致未来(指下一个TM区间)进一步的花费下降。

由于产出(output)不再视为给定，需要在TM的基础上修改理论：(1)就业水平（在工资率固定时等同于产出）取决于继续扩张产能能否带来更大收益；(2)消费函数，即消费支出E-S与总支出E的关系。边际消费倾向(marginal propensity to consumption，MPC)的概念出现了，且被假定为小于1。企业家出现负利润(-ΔQ，or Q<0)，会导致产出和收入的下降(-ΔO, -ΔE), 在MPC影响下逐渐收敛(注意，这里的分析已含乘数论思想)，至最终Q=0，达到另一个TM均衡。

需要说明的是，这里的调整区间(adjustment period)比TM区间长：在TM的分析中，产出无法调整，额外利润产生变化趋势(tendency to change)；而在GT区间内，产出可以调整至均衡水平，使Q=0。但这里的均衡与充分就业无关，任何一个产出水平都可能达到稳定均衡，只要在当时的利率水平下，储蓄等于投资。

储蓄等于投资？JMK对储蓄与投资间关系的观点不同于古典学者。后者认为投资自然来自储蓄，储蓄自然提供投资，两者由利率联系，即为恒等；JMK认为储蓄和投资是分离的，之间并无逻辑联系，利率也不具备调整两者至均衡的能力。仅在储蓄等于投资这一“凑巧”的特殊情况下，利润为零，经济处于(无变化趋的)短期均衡之下，是为储蓄等于投资。

最佳产出水平(optimum level of output)是指无非自愿失业条件下的产出水平，这一定义被正统经济学理论用来分析劳动力市场均衡。正统理论认为存在自然力量(natural forces)使在暂时力量影响下偏离的产出回归最佳水平。这些理论与凯恩斯理论的主要分歧在于：前者强调储蓄对投资和产出的重要性，典型的可贷资金理论(loanable fund theory)；后者则认为投资是关键，投资决定产出水平和储蓄。而投资既可由闲置的储蓄融资，也可以通过增加产出后新创造的储蓄融资，这不是一个关键问题。

在1933年的通论草稿中，JMK从“制度”角度分析了其理论与前人的不同处。古典经济学家假设生产要素自然而然地需要并且获得与其在生产中付出相应的回报，这一结论，无论在加入货币后，还是考虑了其他形式财富（比如储蓄）的情况下，都无任何改变。有三种类型的社会，(1)真实工资经济(real wage economy)，或称合作经济(cooperative economy)，无货币存；(2)中性经济(neutral)，即存在货币，但某种“机制”使资源配置情况完全等同于第一类社会；(3)货币工资经济(money wage economy)，或者企业家经济(entrepreneur economy)，即工资以货币支付，但不存在上述“机制”。显然，JMK是制度经济学的先驱，他坚持认为，制度(货币的存在)必然影响资源配置。企业家经济的核心是企业家关心的是企业的货币收入，而非古典学者假设的：关心实物收入的多寡。

The New Argument

为进一步讨论“最终”均衡，JMK引入quasi-rent代替TM中的利润*，而企业家行为则可用最大化quasi-rent来描述，即，使边际生产成本等于预期价格的产出水平，MC=E(P)。有效需求(effective demand)等于quasi-rent与prime cost(支付给工人的薪金，不同于TM中的total cost)之和，即D=Q+N*W。注意JMK所谓的均衡，意在经过调整过程企业家的价格预期被现实印证，使意料外利润消失，即E(P)=P；不同于古典学者的假设，边际产出收益(marginal revenue of product) dD/dN恒等于劳动的边际负效用(marginal disutility of labour, 即边际生产成本)。预期有效需求(F+I)上升，亦即TM中过度投资(I-S)上升，企业家预期利润上升，产出水平和就业量上升。重要之处在于就业量取决于企业家最大化(I-S)的尝试。

在有效需求D的定义中，消费品和资本品的根本区别在于，前者消费时间很快，不足以产生持久的利息。1934年，JMK明确强调均衡（预期实现）的重要性，有显然有别于TM。他认为预期错误可能发生，但很快即会被修正。接着他引入了就业函数：N=N1+N2=f1(N)+f2(r,e)，其中第一项代表消费部门，第二项代表投资部门。在消费一项中利率变量被剔除了，因为凯恩斯发现短期内消费对利率变化不敏感。上式是通论中Y=C(Y)+I(r)的原型。

*整理自Dr. Joe Chan的课堂笔记*

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关于quasi-rent意义的讨论
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Dear Dr. Chan, I have a question concerning the quasi-rent in ‘JMK arguing towards the General’. In the part of “THE NEW ARGUMENT”, it is said the concept quasi-rent is invented to replace profit in TM. I’m quite confused what it actually means. Does it include the expected reward to entrepreneur, which is a part of total cost in TM, or it simply stands for Q, the unexpected profits in TM? If the latter, how could it be maximized when it is unknown? Here’s some alternatives of explanations, each of which I have some questions and doubts. On the other hands, they may be all wrong.

1.The so-called quasi-money here does not 100% equal to profit in TM in a sense that it also includes expected rewards to entrepreneur, or ‘rent’. Quasi-rend plus wage cost equals effective demand according to GT. Thus the maximization problem simply means to maximize the sum of expected and unexpected rewards to entrepreneur. Since the unexpected profit is unknown, it is treated as given, therefore, the maximization problem remain the same as that in TM. This argument seems plausible but does not consistent with paragraph 3, which claims entrepreneurs attempt to maximize I-S, how?

2.The price level itself is not exogenous according to the fundamental equations. Entrepreneurs could effectively determine price level by choose different level of I-S so as to maximize the unexpected profit, Q in TM. It is probably the most plausible argument in the four because ‘… is determined by the efforts of the entrepreneurs to maximize the excess of investment over saving as defined in my TM.’ But my question to this explanation is that how a single entrepreneur could decide investment (and consumption) decisions of the whole society? What kind of profit (expected or not) are they maximizing?

3.The quasi-money equals to the (unexpected) profit to entrepreneur in TM, the Q. It is still unexpected because the profit has not been materialized. Once the result comes out, if that profit is verified by the fact, it is no longer the profit in TM sense because it has already been correctly expected. In that background, it could be maximized in current stage. But this argument sounds weird due to change of definition in two periods.

4.The discussion is limited in equilibrium i.e. I=S and fulfilled expectation, as stated in paragraph 4. Then there’s not actual profit in TM sense. The quasi-money means fulfilled reward to entrepreneur, which is a part of total cost of production in TM. If so, what does it mean ‘JMK replaces profit with quasi-rent.’

Dear Yiqing: Rent in GT is the same as "profit" in modern micro textbook.  The expected return to entrepreneur in TM is different from the expected return to entrepreneur in GT.  In TM, such expected return constitutes a fixed cost of production.  In GT, expected return is removed from the production cost; expected return = rent.  In your point 4, the last quotation means that the demand price is fully anticipated by producers, who herefore produce an output level such that the demand price (AD) equals the supply price (AS). JC.