ABSTRACT
Giovanni Sartori has defined a party system as the system of interactions resulting from inter-party competition, and has stressed the importance of the (inter)actions as being the units of which the system is composed. Political parties themselves do not belong to the party system; it is their mutual relationships that give birth to the system. 1 The concept of a system in general, and thus of a party system, enables us to delimit the subject of the analysis. A system would not be a system if it did not have a boundary. We know what is inside and what is outside the system.
