What Each Policy Does and How

Monetary policy and fiscal policy are the two principal instruments of macroeconomic management in modern economies. They differ fundamentally in how they work, who controls them, and what they can and cannot accomplish -- but both aim at the same underlying objectives: maintaining stable prices, supporting high employment, and sustaining economic growth.

Monetary policy is conducted by the Federal Reserve through three primary instruments: the federal funds rate, open market operations, and large-scale asset purchases (quantitative easing). All of these instruments work through financial markets. When the Fed cuts rates, it lowers the cost of borrowing throughout the economy -- cheaper mortgages, lower business loan rates, reduced credit card rates. The Fed's decisions do not directly put money in workers' pockets or fund government programs; they change the price of credit, which changes the incentives of private borrowers and lenders, which eventually changes spending, investment, and employment. This transmission mechanism is powerful but indirect, and it depends critically on the private sector's willingness to borrow and invest.

Fiscal policy is conducted by Congress and the President through taxation and spending decisions. It can operate through automatic stabilizers -- mechanisms that expand government deficits in downturns (unemployment insurance, lower income tax revenues) and contract them in expansions without any legislative action -- or through discretionary measures requiring specific legislation. The fundamental difference from monetary policy is that fiscal policy can inject purchasing power directly into the economy: a government that hires workers, builds infrastructure, or sends checks to households creates demand that does not depend on any private actor's willingness to borrow or invest (Blinder, 2016).

Monetary policy works through credit channels that require a willing private sector. When the private sector is shell-shocked and unwilling to borrow at any interest rate, only fiscal policy can close the demand gap. This is the situation Keynes described, and it is the situation the United States faced in 2008.Adapted from J. Bradford DeLong and Lawrence Summers, Brookings Papers (2012)

This difference in transmission has a critical practical implication. Monetary policy is most effective when credit markets are functioning normally and the private sector is capable of and willing to borrow. In severe downturns -- when firms refuse to invest regardless of borrowing costs and households focus on paying down debt rather than taking on new obligations -- monetary stimulus loses traction. Fiscal policy, which does not depend on private sector borrowing decisions, can be effective precisely when monetary policy cannot. The institutional assignment of these two instruments therefore matters enormously: the Fed can move quickly and without political negotiation, but it may be pushing on a string; Congress can deploy the more effective instrument but faces delays, compromises, and ideological constraints that often reduce its speed and scale.

The Tinbergen principle -- that you need at least as many independent policy instruments as you have policy objectives -- clarifies why neither instrument alone is sufficient. An economy that wants simultaneously to maintain full employment, stabilize prices, sustain external balance, and achieve distributional equity cannot accomplish all four objectives with one instrument. The assignment problem is both technical and political: who controls which instrument, for what objectives, with what accountability, and how conflicts between them are resolved are institutional questions as much as economic ones (Mundell, 1962).