Simple (philosophy)

In contemporary mereology, a simple is any thing that has no proper parts. Sometimes the term "atom" is used, although in recent years the term "simple" has become the standard.

Simples are to be contrasted with atomless gunk (where something is "gunky" if it is such that every proper part has a further proper part). Necessarily, given the definitions, everything is either composed of simples, gunk or a mixture of the two. Classical mereology is consistent with both the existence of gunk and either finite or infinite simples (see Hodges and Lewis 1968).

Given a mereology containing the null individual, no object other than the null individual would be simple.

Mirroring the Special Composition Question is the Simple Question. It asks what the jointly necessary and sufficient conditions are for x to be a mereological simple. In the literature this question explicitly concerns what it is for a material object to lack proper parts, although there is no reason why similar questions cannot be asked of things from other ontological categories.

There have been many suggested answers to the Simple Question. Answers include that x is a simple if and only it is a point-sized object; that x is a simple if and only if it is indivisible; or that x is a simple if and only if it is maximally continuous. Kris McDaniel has argued that what it is for an object to be a simple is a matter of brute fact, and that there is no non-trivial answer to the Simple Question (2007b).

Of those philosophers who believe the material world contains simples, there has recently been debate over whether there can be extended simples (see Braddon-Mitchell and Miller 2006, Hudson 2006, Markosian 1998, 2004, McDaniel 2007a, 2007b, McKinnon 2003, Parsons 2000, Sider 2006, Simons 2004 inter alia). An extended simple is (i) a material object; (ii) simple, and (iii) it occupies an extended region of space.

Various reasons have been offered in favor of the claim that extended simples are possible, including: (a) that they are conceivable (Markosian 1998), (b) that purportedly plausible modal principles claiming, roughly, that there are no necessary connections between distinct existences entail their possibility (McDaniel 2007a, Saucedo 2009, Sider 2006), and (c) that contemporary physical theories entail that there are extended simples (Braddon-Mitchell and Miller 2006). One might also argue in favor of the possibility of extended simples by noting that their existence is consistent with the answer to the Simple Question one endorses. In the literature, however, the reasoning is often reversed: Those who think that extended simples are possible often use their purported possibility to argue against answers to the Simple Question that entail their impossibility and those who think that they are impossible uses their purported impossibility to argue against answers to the Simple Question that entail (or strongly suggest) their possibility.

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