Are Western Party Systems “Frozen”?

Party systems have been perceived for a long time as highly persistent, stable, “frozen” subsystems of the polity. This dominant view has been put forward most eloquently by Lipset and Rokkan (1976) and has been adopted and adapted by others since. This article challenges this view by studying 19 Western party systems over their entire history. I show that in terms of party systems fragmentation, ideological polarization, and instability of the vote, most systems cannot be regarded as stable. Party systems have not been “defreezing” in the last few years; they have never really been frozen.