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Modern central banking rests heavily on an intellectual compromise. New Keynesian economics kept Keynes’s concern with unstable demand, accepted the monetarist warning that careless stimulus produces inflation and rebuilt both ideas from the choices of consumers and firms. The Nobel prize awarded to Robert Hall and Michael Woodford crowns that framework, but it arrives just as war, debt and financial instability are exposing how difficult it is to turn an elegant model into policy.

Building macroeconomics from individual choices

Older Keynesian and monetarist models worked mainly from aggregate relationships: government spending could lift demand, or growth in the money supply could raise inflation. Their weakness was that those relationships might change when policy changed. In response to Robert Lucas’s influential critique, New Keynesians sought “microfoundations” by deriving economic outcomes from how people and businesses behave.

Hall applied this approach to consumption. A rational person cares about spending power over an entire lifetime, not merely today’s pay cheque. Someone expecting higher future income may spend more now, whereas a temporary windfall should mostly be saved. Because only genuinely unexpected news should alter that lifetime calculation, consumption ought to move like a random walk: unpredictable from one period to the next, but following a broadly stable direction.

Woodford focused on interest rates. Drawing on Knut Wicksell, he described a credit economy in which borrowing becomes inflationary when market rates fall below the economy’s “natural” return on investment and deflationary when rates rise above it. A central bank should therefore steer its policy rate toward this neutral level rather than attempt to control the money supply directly or fine-tune every fluctuation in demand.

The model behind the modern central bank

Woodford’s framework also gave central bankers a practical way to think about prices. Firms do not adjust prices continuously, and imperfect competition lets them delay doing so. These “sticky prices” mean that monetary policy can affect real activity in the short run even if money is neutral over longer periods.

The resulting model helped make interest rates the main instrument of monetary policy. It also elevated communication. If a central bank explains how it will respond to stronger inflation or weaker growth, markets can anticipate its reaction and adjust borrowing costs before officials act. Woodford’s 2003 book Interest and Prices became a central-banking touchstone during the Great Moderation, when inflation was low and economic volatility appeared subdued.

Yet the natural rate cannot be observed directly and can shift quickly. An investment surge driven by artificial intelligence, for example, may increase demand for capital and push the neutral rate higher. A central bank can infer the rate only from the economy’s response, so policy risks becoming a moving-target exercise disguised by a precise-looking model.

Where elegant theory meets untidy behaviour

The framework also leaves out important forces. Woodford’s core model gives little role to banks, financial fragility or the way low interest rates can encourage investors to take excessive risks. The financial crisis of 2008 ended the Great Moderation and showed that stable consumer prices did not guarantee a stable financial system.

Hall’s consumers are more disciplined than real ones. People often spend a large share of temporary windfalls and react too slowly to lasting changes in income. What looks like random noise may also contain information about the future. These departures do not erase the value of modelling forward-looking behaviour, but they weaken the claim that a clean theory can reliably predict how households will respond.

Even transparency creates complications. Woodford’s logic favours a clear central-bank “reaction function”, yet Federal Reserve chair Kevin Warsh worries about a hall of mirrors in which markets try to predict the central bank while the central bank reads those same market prices as evidence. Some uncertainty may prevent this feedback loop from replacing independent judgment.

Today’s shocks make that judgment especially important. Pandemics and wars disrupt supply rather than simply weakening demand. Heavy public debts can pressure central banks to contain government borrowing costs instead of inflation. Policymakers must decide how much unemployment, inflation and fiscal strain to tolerate, choices that no neutral interest-rate estimate can settle for them.

Hall and Woodford supplied a durable language for thinking about consumption, expectations and monetary policy. Their Nobel is a recognition of how completely that language reshaped the field. The larger lesson, however, is that New Keynesian economics is a framework for judgment, not an autopilot: political constraints, financial risks and human behaviour still determine whether a theoretically sound policy keeps an economy on an even keel.