Rein Taagepera, considerably assisted by Matthew S. Shugart, is an author and advocate of one of the most interesting methodological approaches in recent years; and this applies not only to political science but also - more broadly - to social sciences based on quantitatively predictive logical models. This method consists of constructing - based on deduction and the principles of logic - a conceptual logical model which is subsequently supposed to be subject to testing by dint of a statistical analysis of empirical data. In this paper, on the basis of an analysis of the works by Taagepera and Shugart on the subject, a comprehensive reconstruction of the said approach shall be conducted. The quantitatively predictive logical model of the number of seat-winning parties in the electoral district shall serve as an exemplary pattern of constructing and - more importantly - it will allow for testing the predictive powers of this sort of models. So far no one has tried to test this model by looking at data from local elections. A large sample of electoral districts obtained from Polish local elections in 2018 gives such a unique opportunity.