Giorgio Lando

First, there is no interesting sense in which mereology is a logical doctrine.

Mereologyphi is a metaphysical doctrine, deeply connected to a specific kind of nominalism that we will try to define in detail.

Second, mereology is not—in any of the ways of construing it—“perfectly understood, unproblematic, and certain,” as Lewis instead emphatically declared it to be

Third, the application of mereological monism to abstract entities raises special concerns.

Mereological monism is not a constraint on what can be stipulated, but a controversial, contentful, interesting, and philosophically motivated metaphysical hypothesis about what is out there.

In a sense, this means that I concede that mereological monism is not absolutely general and absolutely topic-neutral: the categorical divide between abstract and concrete entities makes a lot of difference for mereological monism.

the general thesis of the book is that Classical Extensional Mereology is a highly general theory of parthood and composition.

Analogously, mereological monism is understood as the thesis that there is only one highly general theory of parthood and composition.

Fourth, the so-called thesis of Composition as Identity is not an integral part of mereological monism, and will not be defended in this book.

According to Lewis, “composition […] is like identity.”