The dynamics of political systems are explained by writers in the Schumpetarian tradition in terms of such things as moods, tastes, animal spirits, fashions and irrational impulses. This paper takes the idea of a non-rational choice explanation seriously and explores some of its implications. It develops a model of how voters might behave if their actions were not rational. It shows that, under certain broad conditions, a system made up of voters that act on impulse produces cycles in party support. The analysis also raises some questions about time and continuity in the analysis party support. I also suggest an empirical test of the theory. (C) 2002 Elsevier Ltd. All rights reserved.