Why are some governments able to push through radical welfare state reforms while others, operating in similar circumstances, are not? Why are some ideas more acceptable than others? We present an open functional approach to reform to answer these questions and illustrate it empirically by discussing the drastic reform of the Dutch disability scheme in the early 1990s. Ideas translate a functional pressure that existentially threatens a social insurance system into a drastic welfare state reform, such as a severe tightening of eligibility criteria. Functional requirements constrain the range of ideas that political actors can consider for welfare state reform, although they do not determine which ideas are adopted. But once adopted, ideas influence the reforms pursued. A government's choice of ideas and the political strategies to implement them determine the success or failure of the reform. Blame avoidance strategies mediate vitally between the functional pressure, the idea and the reform.