  Even with reference to the Mason-Dixon line — and, more generally, those boundaries that demarcate adjacent parts of a continuous manifold, as when an individual cognitive agent conceptualizes a black spot as being made of two halves — one can raise the question of their ontological status. Such boundaries reflect to various degrees the organizing activity of our intellect, or of our social practices. And it might be argued that belief in their objectivity epitomizes a form of metaphysical realism that cries for justification. We may, in this connection, introduce a conceptual distinction between natural or bona fide boundaries, which are in some sense objective, i.e., grounded in some physical discontinuity or qualitative heterogeneity betwixt an entity and its surroundings, and artificial or fiat boundaries, which are not so grounded in the autonomous, mind-independent world (B. Smith 1995, building on Curzon 1907). Geo-political boundaries such as the Mason-Dixon line are obviously of the fiat sort, and on closer inspection it appears that even the surfaces of ordinary material objects such as apples and tables involve fiat articulations of some kind. So the question is, are there any bona fide boundaries? And, if not, is the fiat nature of our boundary talk a reason to justify an anti-realist attitude towards boundaries altogether? (Compare also how the issue arises in the realm of abstract entities: Are there concepts that carve the world “at the joints”, as per Plato's recipe in the Phaedrus 265e?)