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Can Supply Shocks Be Inflationary with a Flat Phillips Curve?

Author

Listed:
  • Jean-Paul L'Huillier

    (Brandeis University)

  • Gregory Phelan

    (Williams College)

Abstract

Not in standard models. With conventional pricing frictions, imposing a flat Phillips curve also imposes a price level that is rigid with respect to supply shocks. In the New Keynesian model, price markup shocks need to be several orders of magnitude bigger than other shocks in order to fit the data, leading to unreasonable assessments of the magnitude of the increase in costs during inflationary episodes. To account for the facts, we propose a strategic microfoundation of shock-dependent price stickiness: prices are sticky with respect to demand shocks but flexible with respect to supply shocks. This friction is demand intrinsic, in line with narrative accounts for the imperfect adjustment of prices. Firms can credibly justify a price increase due to a rise in costs, whereas it is harder to do so when demand increases. Supply shocks, including productivity shocks, lead to a flexible price allocation, where inflation rises rapidly and output falls. An output gap ensues only if monetary policy is tightened.

Suggested Citation

  • Jean-Paul L'Huillier & Gregory Phelan, 2025. "Can Supply Shocks Be Inflationary with a Flat Phillips Curve?," International Journal of Central Banking, International Journal of Central Banking, vol. 21(2), pages 77-145, April.
  • Handle: RePEc:ijc:ijcjou:y:2025:q:2:a:3
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    References listed on IDEAS

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    Cited by:

    1. Harding, Martín & Lindé, Jesper & Trabandt, Mathias, 2023. "Understanding post-COVID inflation dynamics," Journal of Monetary Economics, Elsevier, vol. 140(S), pages 101-118.
    2. Pablo Cuba-Borda & Jean-Paul L'Huillier, 2025. "Inflation is a Supply Phenomenon," Working Papers 137, Brandeis University, Department of Economics and International Business School.
    3. Ginters Buss & Guido Traficante, 2025. "The Return of Inflation: Look-Through Policy Under Incomplete Information," Working Papers 2025/02, Latvijas Banka.

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    More about this item

    JEL classification:

    • E31 - Macroeconomics and Monetary Economics - - Prices, Business Fluctuations, and Cycles - - - Price Level; Inflation; Deflation
    • E52 - Macroeconomics and Monetary Economics - - Monetary Policy, Central Banking, and the Supply of Money and Credit - - - Monetary Policy
    • E58 - Macroeconomics and Monetary Economics - - Monetary Policy, Central Banking, and the Supply of Money and Credit - - - Central Banks and Their Policies

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