Abstract
The overall stability of the party system is usually studied on the basis of system-level aggregates such as electoral volatility or the effective number of political parties. Such an approach can be problematic, because it primarily measures just one dimension of stability, which is defined as the stability of electoral support.
The article argues that this external dimension of stability should be further analysed in the context of the development of intra-party structures. The institutionalisation theory includes both dimensions, so it is capable of interpreting complex relations between them.
Based on empirical data, the article systematically compares nine relevant political parties in the Czech Republic to better understand differences in the stabilisation of different types of party organisations in the context of party system changes in recent years.