John Maynard Keynes

John Maynard Keynes founded modern macroeconomics and disproved the classical doctrine of automatic full-employment equilibrium. Prior to The General Theory (1936), classical economic orthodoxy was anchored by Say's Law ("supply creates its own demand") and the Quantity Theory of Money ($MV = PY$), which asserted that prices and flexible wages automatically clear labor and goods markets, rendering involuntary unemployment theoretically impossible.

Keynes formulated an alternative macroeconomic architecture based on four foundational pillars: 1. The Primacy of Effective Demand: National income ($Y$) and employment ($N$) are determined by aggregate effective demand, not by production capacity or aggregate supply constraints. 2. Liquidity Preference & Radical Uncertainty: Under unquantifiable Knightian uncertainty, money functions not merely as a medium of exchange, but as a store of value. Speculative demand for liquidity breaks the automatic transmission of savings into physical capital investment. 3. Underemployment Equilibrium & Involuntary Unemployment: The macroeconomy can settle into a stable, non-clearing equilibrium with persistent mass unemployment, due to downward nominal wage rigidity and coordination failures. 4. Counter-Cyclical Fiscal Multiplier Intervention: The state must act as the ultimate stabilizer through counter-cyclical deficit spending, public capital investment, and active monetary management.

2.1 The Aggregate Demand Identity & The Keynesian Multiplier

National output and aggregate expenditure in a closed economy are defined by: $$Y = C + I + G$$

Let consumption $C$ be an affine function of disposable income: $$C = C_0 + c Y_d = C_0 + c(Y - T)$$ where: - $C_0$ is autonomous consumption ($C_0 > 0$). - $c = \frac{dC}{dY} = \text{MPC}$ is the Marginal Propensity to Consume ($0 < c < 1$). - $s = 1 - c = \text{MPS}$ is the Marginal Propensity to Save.

Substituting consumption into the national income identity (assuming lump-sum taxes $T$ and exogenous investment $I$ and government outlay $G$): $$Y = C_0 + c(Y - T) + I + G \implies Y(1 - c) = C_0 - cT + I + G$$ Solving for equilibrium income $Y^*$: $$Y^* = \frac{1}{1 - c} [C_0 - cT + I + G] = k \cdot A$$ where $k = \frac{1}{1 - c} = \frac{1}{\text{MPS}}$ is the Keynesian Expenditure Multiplier.

A marginal increase in public investment $\Delta G$ generates an amplified expansion in total equilibrium output: $$\Delta Y = k \cdot \Delta G = \frac{1}{1 - \text{MPC}} \Delta G$$ For $\text{MPC} = 0.80$, $k = 5.0$, meaning $\$1.00$ of government spending induces $\$5.00$ of cumulative national output.

2.2 Liquidity Preference Theory of Interest

Keynes demolished the classical theory that the interest rate equilibrates saving and investment. Instead, the rate of interest $r$ is a strictly monetary phenomenon determined by the supply and demand for liquidity: $$M_s = M_d(Y, r) = L_1(Y) + L_2(r)$$ where: - $L_1(Y)$ represents transactions and precautionary demand ($\frac{\partial L_1}{\partial Y} > 0$). - $L_2(r)$ represents speculative portfolio demand ($\frac{\partial L_2}{\partial r} < 0$).

When the nominal interest rate falls to an irreducible lower bound ($r \to r_{\text{min}}$): $$\lim_{r \to r_{\text{min}}} \frac{\partial L_2}{\partial r} = -\infty$$ The speculative demand becomes perfectly elastic (horizontal)—the Liquidity Trap. In this regime, open-market monetary expansion fails to lower interest rates further, rendering monetary policy impotent and leaving fiscal expansion as the sole effective policy lever.

2.3 The Marginal Efficiency of Capital (MEC) & Animal Spirits

An entrepreneur invests in capital asset $K$ if the present discounted value of expected future cash flows exceeds the replacement supply price $C_s$: $$C_s = \sum_{t=1}^n \frac{R_t}{(1 + \rho)^t}$$ where $\rho$ is the Marginal Efficiency of Capital.

Investment demand proceeds until the MEC equals the prevailing market interest rate $r$: $$I = f(\rho - r), \quad \text{where } \frac{dI}{d(\rho - r)} > 0$$ Because future revenues $R_t$ depend on psychological expectations formed under unquantifiable uncertainty, fluctuations in private investment are driven by sudden shifts in human optimism—"animal spirits"—rather than calculated mathematical probabilities.

2.4 The Paradox of Thrift

Let autonomous desired savings increase: $\Delta S_0 > 0 \implies \Delta C_0 < 0$. $$\Delta Y^* = \frac{1}{1 - c} \Delta C_0 = \frac{1}{s} (-\Delta S_0) < 0$$ The resulting decline in aggregate income reduces total induced savings: $$\Delta S_{\text{total}} = s \Delta Y^* + \Delta S_0 = s \left( -\frac{\Delta S_0}{s} \right) + \Delta S_0 = -\Delta S_0 + \Delta S_0 = 0$$ An attempt by the whole community to increase aggregate savings merely drives the economy into a recession without increasing realized net savings.

3.1 The Keynesian Cross (Effective Demand Equilibrium)

Aggregate Expenditure (E)
          ^                                       E = Y (45-degree Line)
          |                                      /
          |                                     /   E = C + I + G
          |                                    /  . - - - - - -
          |                             *E*   / '
          |                                  /
          |                                 /
     E_0 -+--------------------------------/
          |                               /
          |                              /
          +-----------------------------+-----------------------------> Output (Y)
          0                            Y* (Equilibrium)

3.2 The Liquidity Trap Asymptote

Interest Rate (r)
       ^
       |
       |  \
       |   \     Speculative Money Demand Curve L_2(r)
       |    \
       |     \
  r_min+------\================================== (Horizontal Elastic Asymptote)
       |            Liquidity Trap Zone (dM/dr -> infinity)
       +---------------------------------------------> Money Stock (M)

5.1 The 1970s Stagflation Breakdown (The Phillips Curve Failure)

Keynesian orthodoxy assumed a stable negative tradeoff between inflation and unemployment (the Phillips Curve). When the 1973 OPEC oil shock struck, advanced economies experienced simultaneous double-digit inflation and high unemployment (Stagflation), revealing that demand management cannot cure supply-side cost shocks.

5.2 Financial Crowding-Out under Inelastic Money Supply

When government deficit spending ($\Delta G > 0$) is financed via sovereign bond issuance in a non-accommodating monetary environment, loanable funds demand increases interest rates ($r \uparrow$), compressing interest-sensitive private capital investment ($I \downarrow$) and mitigating the multiplier effect.

5.3 Political Asymmetry of Deficit Spending (Public Choice Critique)

Keynes’s prescription demanded fiscal discipline: run deficits in recessions, but run budget surpluses in economic booms. Buchanan and the Public Choice school proved that democratic politicians eagerly adopt deficit spending in downturns but refuse to raise taxes or cut spending in booms, generating secular public debt accumulation.

1. Keynes, J. M. (1919). The Economic Consequences of the Peace. Macmillan & Co., London.
2. Keynes, J. M. (1921). A Treatise on Probability. Macmillan & Co., London.
3. Keynes, J. M. (1923). A Tract on Monetary Reform. Macmillan & Co., London.
4. Keynes, J. M. (1925). The Economic Consequences of Mr. Churchill. Hogarth Press, London.
5. Keynes, J. M. (1930). A Treatise on Money (2 vols.). Macmillan & Co., London.
6. Keynes, J. M. (1936). The General Theory of Employment, Interest and Money. Macmillan & Co., London.
7. Keynes, J. M. (1971–1989). The Collected Writings of John Maynard Keynes (30 vols., ed. Donald Moggridge & Elizabeth Johnson). Cambridge University Press.
8. Skidelsky, R. (1983–2000). John Maynard Keynes (3 vols.: Hopes Betrayed, The Economist as Saviour, Fighting for Britain). Macmillan, London.