Why aggregate income is equal to aggregate expenditure?
One man’s income is another man’s expenditure. The expenditure of buyers on products is, by the rule of accounting, income to the sellers of those products. Every transaction that affects income must affect expenditure. If, for example, a company produces and sells one extra loaf of bread. This transaction will raise total expenditure on bread, but it also has an equal effect on income. If the company produces the extra loaf without hiring any more labour (such as making the production process more efficient), then profit increases. If the company produces the loaf by hiring more labour, then wages increase. In both cases, expenditure and income increase equally.
