Nudge/sludge symmetry: on the relationship between nudge and sludge and the resulting ontological, normative and transparency implications

A recent development within nudge theory is the concept of sludge, which imposes frictions on decision-making. Nascent literature adopts a normative interpretation of sludge: nudge good, sludge bad. However, this normative interpretation leaves much to be desired. A clear definition and treatment of sludge remains absent from this literature, as is a complete understanding of ‘frictions’. Furthermore, the relationship between nudges and sludges is unclear. This paper proposes the concept of nudge/sludge symmetry in an attempt to advance the conceptual understanding of sludge. Building from the definition of a nudge, three types of friction permissible under nudge theory are identified: hedonic, social and obscurant. Sludge is then positioned, in terms of frictions, relative to nudge: nudges decrease relative frictions, sludges increase relative frictions. A consequence of this proposition is nudge/sludge symmetry – where a nudge decreases the frictions associated with a specific option, sludge is simultaneously imposed on all other options available to a decision-maker. Nudge/sludge symmetry subsequently challenges the normative interpretation of sludge, and so a new framework drawing on the literature on nudges in the private sector is offered, with the choice architect placed at the centre. This new approach to sludge and emphasis on the role of the choice architect, in turn, reaffirms the importance of transparency in public policy interventions.