Circular Flow of Income — Injections and Withdrawals
Circular flow of income built on the two-sector core (inner real loop, outer money loop), with withdrawals (saving, taxation, imports) leaving the money flow and injections (investment, government spending, exports) entering it, paired through the financial sector, the government and the rest of the world.
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This diagram extends the two-sector circular flow of income. The core is unchanged: the inner loop is the real flow of factors of production and of goods and services, and the outer loop is the money flow of consumer spending, revenue, factor payments and income. Withdrawals (leakages) are income that is not passed on as spending on domestic firms' output: saving (S), taxation (T) and imports (M). Injections are spending on firms' output that does not come from households' income: investment (I), government spending (G) and exports (X). National income rises when injections are greater than withdrawals, falls when withdrawals are greater than injections, and is in equilibrium when the two are equal.
Key points
- The inner loop is the real flow (factors of production, goods and services) and the outer loop is the money flow (consumer spending, revenue, factor payments, income), exactly as in the two-sector model.
- Withdrawals (leakages) leave the money flow on the households' side: saving (S), taxation (T) and imports (M).
- Injections enter the money flow on the firms' side, as spending on their output: investment (I), government spending (G) and exports (X).
- Each withdrawal is paired with an injection through the same sector: S and I through the financial sector, T and G through the government, and M and X through the rest of the world.
- National income rises when injections are greater than withdrawals (I + G + X > S + T + M), falls when withdrawals are greater than injections, and is in equilibrium when I + G + X = S + T + M.
Exam tip
Learn the three pairs as they are drawn: saving (S) goes to the financial sector, which supplies investment (I); taxation (T) goes to the government, which makes government spending (G); and imports (M) go to the rest of the world, which buys exports (X). Every withdrawal leaves the outer (money) loop on the households' side, and every injection joins it on the firms' side as spending on firms' output. Compare the totals, not the pairs: national income rises when I + G + X is greater than S + T + M, even if, for example, saving is greater than investment.
Common mistakes
Students often expect each pair to balance on its own, for example saving to equal investment, when only total injections and total withdrawals need to be equal for equilibrium. Another slip is swapping imports and exports: spending on imports leaves the circular flow to the rest of the world, while exports bring the rest of the world's spending into it.
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