Background
Historical institutionalism explained that institutions created at critical junctures persist because of path dependence, with Pierson's (2000) increasing returns logic as a leading example. Yet this account treated institutions as long stable periods between crises and missed how they change substantially without major shocks. Thelen (2003, 2004) showed that vocational training institutions in Germany, Britain, the United States and Japan changed bit by bit over long periods, coming to serve different functions.
Four types of change
Mahoney and Thelen (2009) distinguished four types. Displacement removes existing rules and introduces new ones; layering adds new rules on top of existing institutions; drift occurs when rules stay the same but their effects change with the environment; and conversion reinterprets existing rules to serve new purposes. They explained which type emerges by the veto possibilities of the political context and the discretion available in interpreting rules.
Cases and significance
Hacker (2004) analyzed 'policy drift' in the United States, where social insurance was not formally cut but weakened because it was not updated for new risks. Hacker, Pierson and Thelen (2015) stressed that drift and conversion are hidden, making political accountability difficult. By treating institutional change as the cumulative result of power struggles rather than dramatic ruptures, the theory is seen as an important advance in new institutionalism.
FAQ
- What is gradual institutional change in simple terms?
- Institutions can change a lot without big events, by adding rules, leaving them unadjusted or reinterpreting them over time.
- What is drift?
- Drift is when rules stay the same but changes in society alter the institution's actual effects.
Sources reviewed: 2026-10-26
References
- Streeck, W., & Thelen, K. (Eds.). (2005). Beyond continuity: Institutional change in advanced political economies. Oxford University Press. Introduces the main types of change.
- Mahoney, J., & Thelen, K. (2009). A theory of gradual institutional change. In J. Mahoney & K. Thelen (Eds.), Explaining institutional change: Ambiguity, agency, and power (pp. 1–37). Cambridge University Press. The core theoretical chapter.
- Thelen, K. (2004). How institutions evolve: The political economy of skills in Germany, Britain, the United States, and Japan. Cambridge University Press. Skills regimes over time.
- Thelen, K. (2003). How institutions evolve: Insights from comparative historical analysis. In J. Mahoney & D. Rueschemeyer (Eds.), Comparative historical analysis in the social sciences (pp. 208–240). Cambridge University Press. Links path dependence and change.
- Hacker, J. S. (2004). Privatizing risk without privatizing the welfare state: The hidden politics of social policy retrenchment in the United States. American Political Science Review, 98(2), 243–260. Policy drift in the US.
- Hacker, J. S., Pierson, P., & Thelen, K. (2015). Drift and conversion: Hidden faces of institutional change. In J. Mahoney & K. Thelen (Eds.), Advances in comparative-historical analysis (pp. 180–208). Cambridge University Press. Drift and conversion refined.
- Pierson, P. (2000). Increasing returns, path dependence, and the study of politics. American Political Science Review, 94(2), 251–267. Path dependence background.