The aim of this article is to establish the limits of freedom of association of partners in commercial companies. They are determined by a closed catalogue of such companies, because it implies the existence of features of individual types of companies. Therefore, one cannot reconcile oneself with the dominant assessment that these features are determined by the substantively significant elements of the company agreement of a given type. The same assessment should be made of an attempt to establish the characteristics of a company type based on substantively significant elements and selected provisions. Still others wrongly seek answers in the nature of the company. These proposals cannot establish the key features of a given type of company. The solution is provided by the concept of the leading idea and the key features of a given type of company established on its basis.