Abstract

Mereology is as a theory of collective sets (or mereological sums). It was formulated by the Polish logician Stanisław Leśniewski. Collective sets are wholes composed of parts, and the concept of being a collective set itself can be defined with the help of the concept of being a part. Mereology may therefore be considered as a theory of „the relation of a part to the whole” (from the Greek: μέρος – „part”). Leśniewski’s mereology was an untypical conception, for it differed from the standard formulations. However, it can be reformulated in the language of structure theory. In the paper, firstly, I examine existentially neutral theories, in which one may prove the existence of only those mereological sums that it is possible to obtain exclusively via the definition of and fundamental properties of the concept of being a part. Moreover, I examine some existentially involved theories of parts (Grzegorczykian mereology and Leśniewskian mereology). One of the main principles of mereology is the transitivity of the concept being a part. This property is often called into question in the literature. Finally, I present an analysis without the assumed transitivity.