Gunk (mereology)

In mereology, an area of philosophical logic, the term gunk applies to any whole whose parts all have further proper parts. That is, a gunky object is not made of indivisible atoms or simples. Because parthood is transitive, any part of gunk is itself gunk.

If point-sized objects are always simple, then a gunky object does not have any point-sized parts. By usual accounts of gunk, such as Alfred Tarski's in 1929, three-dimensional gunky objects also do not have other degenerate parts shaped like one-dimensional curves or two-dimensional surfaces. (See also Whitehead's point-free geometry.)

Gunk is an important test case for accounts of the composition of material objects: for instance, Ted Sider has challenged Peter van Inwagen's account of composition because it is inconsistent with the possibility of gunk. Sider's argument also applies to a simpler view than van Inwagen's: mereological nihilism, the view that only material simples exist. If nihilism is necessarily true, then gunk is impossible. But, as Sider argues, because gunk is both conceivable and possible, nihilism is false, or at best a contingent truth.

Gunk has also played an important role in the history of topology in recent debates concererning change, contact, and the structure of physical space. The composition of space and the composition of material objects are related by receptacles - regions of space that could harbour a material object. (The term receptacles was coined by Richard Cartwright (Cartwright 1975).) It seems reasonable to assume that if space is gunky, a receptacle is gunky and then a material object is possibly gunky.

The term was first used by David Lewis in his work Parts of Classes (1991). Dean W. Zimmerman defends the possibility of atomless gunk (1996b). See also Hud Hudson (2007).

Arguably, discussions of material gunk run all the way back to at least Aristotle and possibly as far back as Anaxagoras, and include such thinkers as William of Ockham, René Descartes, and Alfred Tarski. However, the first contemporary mentionings of gunk is found in the writings of A. N. Whitehead and Bertrand Russell. and later in the writings of David Lewis. Elements of gunk thought are present in Zeno's famous paradoxes of plurality. Zeno argued that if there were such things as discrete instants of time, then objects can never move through time. Aristotle's solution to Zeno's paradoxes involves the idea that time is not made out of durationless instants, but ever smaller temporal intervals. Every interval of time can be divided into smaller and smaller intervals, without ever terminating in some privileged set of durationless instants. In other words, motion is possible because time is gunky. Despite having been a relatively common position in metaphysics, after Cantor's discovery of the distinction between denumerable and non-denumerable infinite cardinalities, and mathematical work by Adolf Grünbaum, gunk theory was no longer seen as a necessary alternative to a topology of space made out of points. Recent mathematical work in the topology of spacetime by scholars such as Peter Roeper and Frank Arntzenius have reopened the question of whether a gunky spacetime is a feasible framework for doing physics.

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