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Financial frictions—credit constraints, collateral requirements, information asymmetries, and monitoring costs—create powerful feedback loops that amplify real shocks and contribute substantially to business cycle volatility. When adverse shocks reduce collateral values, firms and households face tighter borrowing constraints, reducing investment and spending further and depressing asset prices more. Financial accelerator models show how relatively small shocks to fundamentals can generate large macroeconomic fluctuations through financial channels.
From your study of adverse selection and moral hazard, you know that information asymmetries between borrowers and lenders create problems: borrowers know more about their projects' risks than lenders do, and borrowers may take excessive risks once they have the money. These microeconomic frictions are not just theoretical curiosities — when embedded in macroeconomic models, they become powerful amplification mechanisms that help explain why recessions are often deeper and more prolonged than the initial shocks that trigger them.
The core intuition is the financial accelerator, developed by Bernanke, Gertler, and Gilchrist. Consider a firm that borrows against collateral (its real estate, equipment, or financial assets) to fund investment. Now suppose a mild recession hits, reducing the firm's cash flow and depressing the market value of its assets. With lower collateral values, the firm's external finance premium — the extra cost of borrowing compared to using internal funds — rises, because lenders face greater adverse selection risk and demand compensation. The firm cuts investment. But reduced investment means lower demand for capital goods, which further depresses asset prices, which further tightens borrowing constraints. A modest initial shock cascades into a much larger contraction through this self-reinforcing loop.
The key insight is that the financial system does not merely transmit shocks — it amplifies them. In a frictionless world, a 1% decline in productivity would cause roughly a 1% decline in output. With financial frictions, the same shock can produce a 2–3% output decline because the credit channel multiplies the initial impact. The mechanism also works in reverse during booms: rising asset prices relax borrowing constraints, enabling more investment, which pushes asset prices higher still. This symmetry helps explain why economies exhibit pronounced boom-bust cycles rather than smooth fluctuations around trend.
The 2008 financial crisis provided dramatic validation of these models. A decline in U.S. housing prices — initially a correction in one asset market — cascaded through the financial system via exactly the mechanisms these models describe. Banks holding mortgage-backed securities saw their capital erode, forcing them to cut lending. Firms and households with underwater collateral could not refinance or borrow. The resulting credit crunch turned a housing correction into the deepest global recession since the 1930s. This experience motivated a new generation of DSGE models that incorporate financial frictions as essential features rather than optional add-ons, fundamentally reshaping how central banks think about financial stability and macroprudential policy.