Economics · Ch 4 — Determination of Income and Employment
Aggregate Demand and its Components
Aggregate Demand and its Components
4.1 Aggregate Demand and Its Components
The terms consumption, investment, and total output of final goods (GDP) appear in two different senses. In the chapter on National Income Accounting, they were used as actual or accounting values — what the economy really did in a given year. These are called ex post measures: they record what has already happened.
But to understand how income and employment are determined, we need a different perspective. We need to know what people, firms, and the government plan to do — their intended spending, not what they end up doing. These planned values are called ex ante measures.
Ex ante = planned (before the fact). Ex post = actual (after the fact). The distinction is crucial: income determination theory works with ex ante values, while national income accounting works with ex post values.
Why the Distinction Matters: An Example
Consider a producer who plans to add ₹100 worth of goods to her inventory by the end of the year. Her planned investment — the ex ante value — is ₹100.
Now suppose an unexpected surge in demand occurs. Customers buy more than she anticipated, and she has to sell goods worth ₹30 from her stock to meet this extra demand. At the end of the year, her inventory has increased by only ₹70 (₹100 planned addition minus ₹30 sold from stock). Her actual investment — the ex post value — is ₹70, not ₹100.
The planned investment was ₹100, but actual investment turned out to be ₹70. The difference arose because actual sales exceeded planned sales. This gap between planned and actual values is exactly what drives changes in output and income in the economy.
Do not confuse planned investment with actual investment. In the example, the producer planned to invest ₹100 but actually invested only ₹70. The ₹30 worth of goods sold from inventory represents unplanned disinvestment — a reduction in stock that was not part of the original plan.
The Components of Aggregate Demand
To determine the equilibrium level of income, we must examine the planned values of each component of aggregate demand. This chapter works with a two-sector model — an economy made up only of households and firms — so aggregate demand has just two components:
- Consumption demand — what households plan to spend on goods and services.
- Investment demand — what firms plan to spend on capital goods and additions to inventory.
Together these give . A government sector (adding government expenditure and taxes ) is brought in only as a brief aside in Section 4.2 and then set aside for the rest of the chapter, while an external sector with net exports belongs to the fuller open-economy model studied later — neither is part of this chapter's framework. …