The discretionary powers of welfare state professionals are in tension with the requirements of the democratic Rechtsstaat. Extensive use of discretion can threaten the principles of the rule of law and relinquish democratic control over the implementation of laws and policies. These two tensions are in principle ineradicable. But does this also mean that they are impossible to come to grips with? Are there measures that may ease these tensions?We introduce an understanding of discretion that adds an epistemic dimension (discretion as a mode of reasoning) to the common structural understanding of discretion (an area of judgment and decision). Accordingly we distinguish between structural and epistemic measures of accountability.The aim of the former is to constrain discretionary spaces or the behaviour within them while the aim of the latter is to improve the quality of discretionary reasoning.The focus in this article is on epistemic measures that are internally related to the main characteristic of accountability, namely justified use of discretionary power.What characterizes many welfare-state arrangements is that they confer discretionary powers upon professionals in their roles as 'street-level bureaucrats'. 2 Professionals then act as gatekeepers, deciding who gets what, when, and how. This fact has generated its share of criticism. 3 The discretionary powers of welfare-state professionals are troublesome for two main reasons. First, there is a tension between discretion and the formal demands of the rule of law. Extensive use of discretion in the application of law can threaten the principles of predictability, legality and equal treatment. Second, there is a tension between discretion and democratic control. Discretion is the black hole of democracy -to borrow Bo Rothstein's metaphor. 4 Entrusting street-level bureaucrats with extensive discretionary powers is by definition almost equal to relinquishing democratic control over these final steps.There is, of course, a lot of sloppy discretionary work. But that is not our point and not what basically makes discretion problematic from the point of view of rule of law and democracy. The two tensions are intrinsic and cannot be removed, only ameliorated. They follow from the very nature of discretion as a judgmental and decisional activity and can appear even if we presuppose that the activity is performed in a conscientious manner. 5 Our guiding idea is that discretion has both a structural and an epistemic aspect. On the one hand it designates a space where an agent has the autonomy to judge, decide and act according to his own judgment. In this sense discretion is an 'opportunity-concept'. On the other hand it designates the kind of reasoning that results in conclusions about what to do under conditions of indeterminacy. In this sense it is an 'exercise-concept'. 6