In modern literature the concept of party system is interpreted ambiguously
(a) Party system - a concept for the mechanism of interaction and competition between parties in the struggle for power and its implementation, which is characterized by the following features
1) ratio of parties with different political status;
2) a certain degree of stability of inter-party relations;
3) a certain nature of inter-party relations
(b) The party system is a concept for a set of parties in a given country, which is characterized by the following features
1) the specific number of parties;
2) certain socio-political and legal conditions;
real opportunities to gain power
The study of party systems in comparative political science at the empirical level is based on the search for dependencies between party systems at the electoral level (parties participating in elections) and at the parliamentary level (parties having their representatives in parliament). Factors that determine the level of party fragmentation (or factionalization) of parliaments are also studied.
Comparative political science uses the following theoretical models, which determine the factors that determine the quantitative parameters of party systems.
1. the institutional model ("single-round simple majority system" - with a relative majority rule for single-mandate constituencies). The logic of this approach is that such an electoral system leads to the formation of a virtually bipartisan system: although in fact there are other political parties in addition to the two, they do not play a significant role and do not define the political process (M. Duvergé).
2. Social model (the model of "stabilization of European party systems"). Party systems are affected by the level of fragmentation of social structures, social relations between different groups of the population connected with social differentiation, as parties represent special interests and conduct them to the parliament through the process of delegation (Lipset, Roccan).
3. a model combining the data of institutional and social models. This model distinguishes the peculiarities of the electoral system, social differentiation of the society and the form of state governance (Powell, O. Neto and G. Kons) as the factors determining the quantitative parameters of party systems.
In political science, there are three types of party systems: single-party, double-party and multi-party.
A single-party system is characteristic only of totalitarian and authoritarian regimes. In the case of a single-party system, the ruling status (actual or legal) is assigned to one party. Political science is distinguished:
(a) Single-party systems in the strict sense of the word, which exclude even the nominal existence of other parties; in fact, such parties are part of the state apparatus;
b) in fact, single-party systems ("artificial multiparty system") disguised as multiparty system; they carry out total ideological and organized control of the state party.
The bipartisan political system is characterized by two strong parties in the political system of society, which are periodically replaced by each other in power. Such a system does not exclude the participation of other political parties in the political process, which can sometimes have a major impact on the political balance in society, but these parties never come to power themselves.
Therefore, there are two types of bipartisan systems:
(a) The classical variant, where the main parties collect up to 90% of the votes of the electorate, thus depriving the other parties of access to power.
b) the system of "two and a half parties", in which a third, less powerful, but able to influence the outcome of the struggle for power appears next to the two main parties. By supporting one of the main parties, this third party influences the ultimate success of one of the strong parties and thus defines the contours of the government coalition.
In a multiparty system, more than two parties have enough organization and influence to influence the functioning of government institutions. Multiparty systems are divided into the following:
a) party systems of "polarized pluralism", which are characterized by anti-systemic parties opposing the existing social and economic system; bilateral opposition (opposition to the government on both the left and right sides); central position of one or a group of parties; polarization as a result of significant ideological division; prevalence of centrifugal tendencies over centrifugal tendencies and, as a consequence, weakening of the center;
b) party systems of "moderate pluralism", where three to five parties compete and none of them can be in power on their own, resulting in coalition governments; such a system lacks anti-systemic parties and bilateral opposition; there is little ideological distinction between parties; there is centripetal competition; parties are oriented towards participation in government.