in the faculty of law and economic sciences in Paris, 1955 to 1985, and contributed to Libération and Le Monde. From 1989 to 1994, he sat in the European Parliament as an MEP for the Italian Communist Party. In 1946 he expanded his theses, with a special interest in the relation between electoral systems and party systems. This interest is at the heart of his most important publication: "The Political Parties" (1951). The work is one of the classics of party research, translated into several languages. That thesis led to Duverger's law, and later he coined the term "semi-presidentialism" and "semi-parliamentarism". Political parties Having as a point of reference their structure, Duverger in his book Les Partis Politiques (1951) distinguished parties between elite-based parties and mass-based parties. Elite-based parties rather prefer the quality of their members over their quantity, their affiliates being people of great influence on local or national scale. They have flexible and disorganized structures, in general are weakly disciplined and lack developed pragmatic content, allowing each of their members to benefit from an enormous freedom of action. Their funding is generally provided by a sponsor, and as their strength comes from their elected representatives, they are typical parties of parliamentarian creation, which depend on the reputation and support of their benefactors. Mass-based parties possess a secure organization and a strong structure arranged as a pyramid, with superposed hierarchically-arranged levels. Their members identify themselves more with the party's ideology than with its leader, so they have an abstract adhesion. Their decisions are based on the participation of each one of its members, and its founding is granted by their members' payments, a situation that leads them to gain as many adherents as possible. These parties tend to develop on a par with suffrage and democracy. For instance, elite-based parties execute an often sporadic political labor, focused on elections. However, the disadvantage this implies in relation to their contestant parties (which denote permanent labor and a disciplined and organic structure), impels them to modify their organization to become mass-based parties. Duverger's Law With discovery attributed to Duverger, he observed the effect and recorded it in several papers published in the 1950s and 1960s. In the course of further research, other political scientists began calling the effect a "law" or principle. Duverger's law suggests a nexus or synthesis between a party system and an electoral system: a proportional representation (PR)