What is Keynsian economics, pt 3

From Wikpedia:

Keynes and the Classics
Keynes sought to distinguish his theories from and oppose them to "classical economics," by which he meant the economic theories of David Ricardo and his followers, including John Stuart Mill, Alfred Marshall, Francis Ysidro Edgeworth, and Arthur Cecil Pigou. A central tenet of the classical view, known as Say's law, states that "supply creates its own demand". Say's Law can be interpreted in two ways. First, the claim that the total value of output is equal to the sum of income earned in production is a result of a national income accounting identity, and is therefore indisputable. A second and stronger claim, however, that the "costs of output are always covered in the aggregate by the sale-proceeds resulting from demand" depends on how consumption and saving are linked to production and investment. In particular, Keynes argued that the second, strong form of Say's Law only holds if increases in individual savings exactly match an increase in aggregate investment.

Keynes sought to develop a theory that would explain determinants of saving, consumption, investment and production. In that theory, the interaction of aggregate demand and aggregate supply determines the level of output and employment in the economy.

Because of what he considered the failure of the “Classical Theory” in the 1930s, Keynes firmly objects to its main theory—adjustments in prices would automatically make demand tend to the full employment level.

Neo-classical theory supports that the two main costs that shift demand and supply are labor and money. Through the distribution of the monetary policy, demand and supply can be adjusted. If there were more labor than demand for it, wages would fall until hiring began again. If there was too much saving, and not enough consumption, then interest rates would fall until people either cut their savings rate or started borrowing.

Wages and spending
During the Great Depression, the classical theory defined economic collapse as simply a lost incentive to produce, and the mass unemployment as a result of high and rigid real wages.

To Keynes, the determination of wages is more complicated. First, he argued that it is not real but nominal wages that are set in negotiations between employers and workers, as opposed to a barter relationship. Second, nominal wage cuts would be difficult to put into effect because of laws and wage contracts. Even classical economists admitted that these exist; unlike Keynes, they advocated abolishing minimum wages, unions, and long-term contracts, increasing labor-market flexibility. However, to Keynes, people will resist nominal wage reductions, even without unions, until they see other wages falling and a general fall of prices.

He also argued that to boost employment, real wages had to go down: nominal wages would have to fall more than prices. However, doing so would reduce consumer demand, so that the aggregate demand for goods would drop. This would in turn reduce business sales revenues and expected profits. Investment in new plants and equipment—perhaps already discouraged by previous excesses—would then become more risky, less likely. Instead of raising business expectations, wage cuts could make matters much worse.

Further, if wages and prices were falling, people would start to expect them to fall. This could make the economy spiral downward as those who had money would simply wait as falling prices made it more valuable—rather than spending. As Irving Fisher argued in 1933, in his Debt-Deflation Theory of Great Depressions, deflation (falling prices) can make a depression deeper as falling prices and wages made pre-existing nominal debts more valuable in real terms.