The United States consistently runs a large trade deficit. Which explanation is most consistent with the national accounts identity TB = S − I?
AUS goods are too expensive relative to imports, so Americans buy foreign products instead
BUS corporations are less efficient than foreign competitors, making US exports uncompetitive
CUS domestic investment persistently exceeds US domestic saving, requiring capital inflows whose accounting counterpart is a trade deficit
DThe US government imports too much, creating a structural spending-driven deficit
The identity TB = S − I means trade deficits are fundamentally a macroeconomic savings-investment phenomenon, not a competitiveness problem. When domestic investment exceeds domestic saving, the country must draw in foreign capital — and a net capital inflow is the accounting mirror of a trade deficit. The US has run persistent deficits partly because its investment rate consistently exceeds its saving rate and because US financial assets attract foreign capital. Tariffs and competitiveness improvements cannot override this accounting identity.
Question 2 Multiple Choice
A country runs a $50 billion trade surplus this year. According to the identity TB = S − I, what must also be true?
AThe country's government is running a budget surplus of at least $50 billion
BThe country is saving more than it is investing domestically, and is a net lender to the rest of the world
CThe country's currency must be undervalued, making its exports cheaper on world markets
DThe country has higher interest rates than its trading partners, attracting net capital inflows
TB = S − I means a positive trade balance requires S > I. The surplus saving must go somewhere — it is lent to or invested abroad, making the country a net creditor. This is an accounting identity, not an empirical claim: it must be true by definition, regardless of the country's currency value or interest rates. Those factors may explain why saving exceeds investment, but the identity holds regardless of mechanism.
Question 3 True / False
By accounting identity, a country running a persistent trade deficit is simultaneously a net borrower from the rest of the world — the capital account surplus exactly mirrors the current account deficit.
TTrue
FFalse
Answer: True
Every dollar of trade deficit (more imports than exports) corresponds to a dollar of net capital inflow — foreigners are lending to or investing in the country to finance the excess spending. The capital account and current account always sum to zero by construction. A trade deficit is not just a statement about goods flows; it is simultaneously a statement about financial flows. The deficit country is importing capital.
Question 4 True / False
A trade deficit generally signals economic weakness because it means a country is consuming more than it produces and cannot compete in global markets.
TTrue
FFalse
Answer: False
Whether a deficit is problematic depends on what drives it. A deficit driven by high domestic investment — attracting foreign capital to fund productive capacity — can be growth-enhancing. The US deficit has persisted partly because US financial assets are attractive to foreign investors, not because American industry is failing. The identity TB = S − I makes clear that deficits reflect the saving-investment gap, not competitiveness alone. The arithmetic is neutral; whether the underlying behavior is sustainable requires separate economic analysis.
Question 5 Short Answer
Explain why imposing tariffs alone is unlikely to eliminate a trade deficit if the underlying cause is that domestic investment exceeds domestic saving.
Think about your answer, then reveal below.
Model answer: Tariffs raise the price of imports and may shift some spending toward domestic goods, but they don't change the national saving-investment gap. The identity TB = S − I guarantees a trade deficit whenever I > S — the gap must be financed by capital inflows, which are the accounting mirror of a trade deficit. Tariffs might change which goods are imported or which countries are traded with, but the aggregate deficit simply shifts to other trading partners. To sustainably close the deficit, a country would need to increase saving (reduce consumption or government deficits) or decrease domestic investment.
Economic research consistently shows that bilateral tariffs can reduce deficits with specific countries, but the overall trade balance barely moves because the underlying saving-investment imbalance remains. The identity is not a suggestion — it is an accounting constraint. This is why trade policy alone is insufficient to address a structurally driven deficit: the macroeconomic fundamentals must change, not just the trade rules.