The classical model and Keynes's challenge

Picture an economy where people want to work but can’t find jobs. The classical answer is that this cannot last: unemployed workers will accept lower wages, firms will hire, and full employment returns. Output is limited by what the economy can produce, its labour, capital and technology. Demand takes care of itself.

Keynes’s answer, in The General Theory (1936), was that money wages don’t fall easily and, even if they did, lower wages mean lower incomes and lower spending. Output is limited by what people want to buy. It can settle below full employment and stay there.

Hyderabad put the dividing line in one phrase: the speed of price adjustment. With fast-adjusting wages and prices you get the classical world; with sticky ones, the Keynesian world.

The classical model builds output from the supply side in three steps.

1. Labour demand. A competitive firm hires another worker as long as that worker adds more to output than he costs in goods. So it hires until the marginal product of labour equals the real wage, W/P. Because the marginal product falls as more workers are added, labour demand slopes down against the real wage.
2. Labour supply. Workers decide how much to work by what the wage buys, the real wage, and how much they value leisure. Not by the money wage: that is the absence of money illusion. JNU 2021 made this its answer: supply depends on the real wage and the preference for leisure, not on the marginal product or the money wage.
3. Output. Where supply meets demand gives employment. The production function turns that employment, with the capital stock and technology, into output. Nothing about demand has entered.

That is why Hyderabad calls the supply-determined nature of output and employment the most crucial feature of the classical system.

Here is a small classical economy: output Y = 2A√L, so the marginal product of labour is A/√L; labour supply is L = 100 × W/P; and the price level comes from the quantity equation with velocity 2. Start with wages flexible and move the money supply. Then switch to a money wage that can’t fall below its starting level of 1, and cut the money supply to 70.

With flexible wages, money only rescales prices and wages: every real quantity stays put. With a floor on money wages, a fall in money lowers prices but not wages, so the real wage rises, firms move up their labour demand curve and hire fewer, and people willing to work at that wage cannot find jobs. That is involuntary unemployment, and money has become non-neutral. Keynesians put the primary reason for this on price and wage stickiness (Hyderabad 2016 and 2018).

As an identity this is always true: spending equals the value of what is bought. The classical quantity theory adds two claims. V is fixed by habits and payment technology, and Y is fixed by the labour market and production function. Then P is proportional to M. Money is a veil over the real economy: it sets the price level and nothing else. This split between the real and the money side is the classical dichotomy, and money’s having no real effect is money neutrality.

Classical macroeconomics combines Say’s law, which settles output, with the quantity theory, which settles prices (Hyderabad 2012). In an AD–AS diagram, more money shifts aggregate demand right, but aggregate supply is vertical, so only prices rise (UGC NET 2025).

Taking growth rates turns the quantity equation into a rule for how fast money should grow:

If output is fixed by supply, what stops too little being spent on it? The classical answer is the interest rate. Saving is a supply of loanable funds and rises with the interest rate; investment is a demand for them and falls with it. The rate adjusts until planned saving equals planned investment (Hyderabad 2018), so every rupee not consumed is spent by someone else. That is the mechanism behind Say’s law.

With a government, split saving into private and public parts:

Now let the government borrow more. Its demand for funds pushes up the interest rate; investment falls and, as saving responds, consumption falls too. With output fixed at full employment, extra government spending is exactly matched by lower private spending: complete crowding out. UGC NET 2025’s correct statements were: the demand for loanable funds shifts right, saving rises by the fall in consumption, and consumption and investment fall by the rise in government spending.

Keynes attacked each classical step.

• Wages. Workers resist cuts in money wages, so the labour market need not clear (JNU 2020). With many people willing to work at the going wage, the labour supply curve is effectively flat at that wage (UGC NET 2023).
• Saving and investment. Saving depends mainly on income, not on the interest rate. Investment depends on expectations of profit, “animal spirits”. They are brought into line not by the interest rate but by changes in income: if investment falls, income falls until people save only as much as is invested. Investment determines saving (JAM 2021). Maurice Dobb’s summary, set by JNU in 2014: the causal emphasis was reversed.
• Output. In the short run firms produce what they expect to sell. Output is set by effective demand, and employment follows from output: employment is determined in the product market (Hyderabad 2010; JAM 2022).

The classical reply was the Pigou effect: if prices keep falling in a slump, the real value of people’s money balances rises, they feel wealthier and spend more, so demand recovers after all (Hyderabad 2018). It works through the wealth effect of money balances, but slowly.

The next lesson turns Keynes’s idea into a model you can solve: the Keynesian cross.

UGC NET has twice asked for these in order, in 2023 and 2025, and CUET asked the year of The General Theory.