Fiat boundaries: how to fictionally carve nature at its joints

Boundaries are the outermost parts of objects, with a twofold function: dividing objects from their environment and allowing objects to touch each other.
The task of this paper is to classify and describe the human dependent boundaries, i.e., the so-called fiat boundaries, on the basis of the seminal work by Smith and Varzi. Roughly, a fiat boundary is a marker of discontinuity between two or more objects which relies on a human function assignment, usually called ‘fiat act’.
In what follow I outline the different ways in which human beings make fiat boundaries out of nature. Along the way I shall give evidence that a theory of fiat boundaries can be useful to take up as a starting point for doing metaphysics and for giving an account of the ontology of both the material and the social world. The chief goal is to shed a light on how some objects depend upon human beings: either in a deliberative or non-deliberative way; either a priori or a posteriori; by means of individual or collective act; by modal strength, namely possible and necessary boundaries.