Giorgio Lando

Another relation is strictly connected to parthood: the relation that connects many things to a single thing that includes whatever is in the many things and nothing extraneous to them; this many-one relation can be dubbed composition.

The thesis is that there is a single, general, exhaustive theory of parthood and composition. This theory, usually called Classical Extensional Mereology

(a) parthood is transitive (if a first thing is part of a second thing, and this second thing is part of a third thing, then the first thing is part of the third as well);

(b) given some things, there is at most one thing composed by them;

(c) given some things, no matter how heterogeneous and disparate they are, there is at least one thing composed by them.

Consider, as a first example, the essential/accidental distinction.

Are some parts of a whole such that their annihilation would annihilate the whole too?

Another example: the supervenience or emergence of the properties of complex entities over the properties and relation of their parts.

According to the narrow understanding of mereology as a discipline I am going to adopt, essentiality, dependence, and supervenience lie beyond the explanatory scope of mereology.

Mereology is only about the formal features of the relation of parthood, and about identity and existence conditions for wholes.