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In mereology, an area of philosophical logic, the term gunk applies to any whole whose parts all have further parts, which themselves all have parts, and so on. That is, a gunky object is not made of indivisible atoms or simples:
If something is made of atomless gunk then it divides forever into smaller and smaller parts—it is infinitely divisible. However, a line segment is infinitely divisible, and yet has atomic parts: the points. A hunk of gunk does not even have atomic parts ‘at infinity’; all parts of such an object have proper parts.
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 concerning 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).
- Sider, Theodore (1993). "Van Inwagen and the Possibility of Gunk" (PDF). Analysis 53: 285–289. doi:10.1093/analys/53.4.285.
- Zimmerman, Dean (editor) Oxford Studies in Metaphysics: Volume 4 (Oup Oxford 2008) Arntzenius, Frank "Gunk, Topology and Measure"
- Cartwright, Richard, 1975, "Scattered Objects", in Keith Lehrer, ed., Analysis and Metaphysics (Dordrecht: Reidel, 1975), pp. 153–171. Reprinted in Philosophical Essays, pp. 171–186.
- Hud Hudson, 2007. "Simples and Gunk", Philosophy Compass 2 (2), pp. 291–302. doi:10.1111/j.1747-9991.2007.00068.x
- Lewis, David, 1970. “Nominalistic Set Theory”, Noûs 4, pp. 225–40. JSTOR 2214424
- Lewis, David, 1991. Parts of Classes, Cambridge: Basil Blackwell.
- Sider, Ted, 1993. "Van Inwagen and the Possibility of Gunk", Analysis. 53(4): 285-289. doi:10.1093/analys/53.4.285, JSTOR 3328252
- Tarski, Alfred, 1929. "Foundations of the Geometry of Solids."
- Zimmerman, Dean W., 1996a. "Indivisible Parts and Extended Objects: Some Philosophical Episodes from Topology’s Prehistory." Monist 79(1). 148–180. JSTOR 27903469
- Zimmerman, Dean W., 1996b. "Could Extended Objects Be Made Out of Simple Parts? An Argument for 'Atomless Gunk'", Philosophy and Phenomenological Research 56: 1-29. JSTOR 2108463