Different Theories of Parts

Stanisław Leśniewski’s mereology was formulated in a specific way, deviating from standard formalizations. Nowadays, Leśniewski’s theory is presented in the form of an elementary theory or translated into the language of the theory of relational structures. In this article, firstly, we look at existentially neutral theories, in which we do not postulate the existence of any other collective sets than those obtained from the definition and the basic properties of the relation of being a part. We also examine some existentially involved theories of parts. Among them, there is Grzegorczykian mereology and Leśniewskian mereology. One of the main principles of mereology is the transitivity of the concept of being a part of. This property is often questioned in the literature on the subject. In the final part, we present problems related to the transitivity of this concept.