Previous work on the evolution of policy mixes has highlighted how these three criteria are often lacking in mixes which have evolved over time as well as those which have otherwise been consciously designed. The paper revisits work by historical institutionalists in order to more clearly assess the reasons why many policy mixes may suffer from inconsistent, incoherent or incongruent elements. The change processes identified in this literature, notably layering, conversion, drift, replacement and exhaustion, all have characteristic effects on policy mixes. However, this literature also contains a characteristic confusion, in which a term such as layering is used to refer to both a process of change and an outcome (a policy mix made up of different elements layered over time). Adding the dimension of 'intentionality' to earlier thinking about processes such as policy layering, drift, conversion, exhaustion and replacement, it is argued, helps to make sense out of these different processes and how they relate to 'design'. Thinking about intentionality also connects this discussion of policy change and policy mixes to contemporary debates about governance and steering.
