The Possibility Principle and the Truthmakers for Modal Truths
Total Page:16
File Type:pdf, Size:1020Kb
View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by University of St. Thomas, Minnesota University of St. Thomas, Minnesota UST Research Online Philosophy Faculty Publications Philosophy 2010 The oP ssibility Principle And The rT uthmakers For Modal Truths Timothy J. Pawl University of St. Thomas, Minnesota, [email protected] Follow this and additional works at: http://ir.stthomas.edu/cas_phil_pub Part of the Philosophy Commons Recommended Citation Pawl, Timothy J., "The osP sibility Principle And The rT uthmakers For Modal Truths" (2010). Philosophy Faculty Publications. 7. http://ir.stthomas.edu/cas_phil_pub/7 This Article is brought to you for free and open access by the Philosophy at UST Research Online. It has been accepted for inclusion in Philosophy Faculty Publications by an authorized administrator of UST Research Online. For more information, please contact [email protected]. Australasian Journal of Philosophy 2010; pp. 1–12, iFirst article THE POSSIBILITY PRINCIPLE AND THE TRUTHMAKERS FOR MODAL TRUTHS Timothy Pawl A necessary part of David Armstrong’s account of truthmakers for modal truths is his Possibility principle: any truthmaker for a contingent truth is also a truthmaker for the possibility of the complement of that contingent truth (if T makes p true and p is contingent, then T makes }*p true). I criticize Armstrong’s Possibility principle for two reasons. First, his argument for the Possibility principle both relies on an unwarranted generalization and vitiates his desire for relevant truthmakers. His argument undercuts relevant truth- makers by entailing that each contingent being is a truthmaker for all modal truths. Second, even if the argument seems successful, the Possibility principle is subject to counterexamples. Armstrong’s being composed of more than fifty atoms makes it true that something composed of more than fifty atoms exists and that truth is contingent, but his being composed of more than fifty atoms does not make it true that it is possible that it is not the case that something composed of more than fifty atoms exists. David Armstrong is the most well-known proponent of truthmaker theory, and his book, Truth and Truthmakers, is the most well-known defence of it. In this book, Armstrong provides his Possibility principle: any truthmaker for a contingent truth is also a truthmaker for the possibility of the complement of that contingent truth (if T makes p true and p is contingent, then T makes }*p true), a principle with which his account of truthmakers for modal truths stands or falls. And, while the book has received much critical attention, this particular principle, which is so important to his work, has received relatively little.1 Furthermore, what attention it has received has been, in all but one problematic case, paid to the argument Armstrong gives for the principle, and not to whether the principle itself is true or false.2 Armstrong has conceded, in the pages of this very journal, that his argument in Truth and Truthmakers was ‘marred by a very bad mistake’ [2006b: 245] 1Cameron [2005], McDaniel [2005], Mumford [2005] and Tallant [2005] all provide careful reviews of the book, but none mentions the Possibility principle. Alward [2004: 76–7] and Bostock [2005: 369] briefly discuss the principle without calling it into question; Hochberg [2006: 187–8] doesn’t argue that the Possibility principle is false, but he does claim that Armstrong does not go far enough in showing how the intrinsicality of contingency should be understood in his argument and that Armstrong must, in the end, appeal to a fundamentally modal entity in his account of truthmakers for modal truths; Keller [2007] argues clearly that Armstrong’s [2004] argument for the Possibility principle is flawed, but does not provide an argument that the principle itself is false; and Simons [2005: 254] claims that the argument is invalid and that the Possi- bility principle is implausible, but offers no reasons for thinking the principle implausible. 2Kalhat [2008] provides the one extant argument for the falsity of the Possibility principle. It is problematic because it, like Armstrong’s [2007: 103] argument, has de re–de dicto confusions. I will discuss this problem later as my second smallish point in x3. Australasian Journal of Philosophy ISSN 0004-8402 print/ISSN 1471-6828 online Ó 2010 Australasian Association of Philosophy http://www.tandf.co.uk/journals DOI: 10.1080/00048400903193353 2 Timothy Pawl and that he ‘certainly made a dreadful hash of arguing’ for it [2005: 271], but he also says that he still thinks the Possibility principle is defensible. He has since given another argument for the Possibility principle, which has yet to be discussed in the literature [2007: 103]. In this paper, I criticize that new argument, then I go on to argue that the Possibility principle is false. Armstrong criticizes both David Lewis and Alvin Plantinga for ontological extravagance in his book, Truth and Truthmakers. He writes, after reference to Lewis and Plantinga: It seems to me very surprising that so many good philosophers consider that huge metaphysical commitments must be made in order to give an account of these truths [of mere possibility]. [2004: 83] He goes on to say that ‘these philosophers are bringing giants to do a boy’s work’ [loc. cit.]. The giants to whom Armstrong refers are well known.3 Armstrong takes Plantinga to seek the ontological grounding of modal truths in abstract possible worlds and haecceities. Lewis argues that at least some modal truths are made true by concrete, unactual worlds and their parts.4 It would be better, all else being equal, if we could ground modal truths without recourse to necessarily existing haecceities or unactual, concrete worlds. Armstrong has attempted to provide truthmakers for modal truths without such ontological bloating. To cure this distention he prescribes the Possibility principle. If Armstrong’s account of truthmakers for modal truths were successful, it would be of no small significance. For, if successful, it removes a strong incentive to carry the heavy ontological burden that Plantinga and Lewis hold.5 If Armstrong can show that we can ground modal truths without the costs associated with Lewis and Plantinga’s ontologies, he has done a great service to modal metaphysics. He will have, to use his own words, splashed ‘cold water on the need for the wildly ambitious truthmakers that have been proposed by a number of contemporary metaphysicians’ [2004: 85]. I criticize Armstrong’s attempted ontological grounding for modal truths on two grounds. First, I claim that his argument for the Possibility principle is weak. As presented in Truth and Truthmakers, it is unsound. Armstrong has recognized this infelicity and attempted to amend it. His emendation, however, has two problems of its own. It requires an unwarranted general- ization and it runs counter to Armstrong’s stated desire for relevant truthmakers. Second, even if the argument seems successful, the Possibility principle is subject to counterexamples. Armstrong makes it true that something composed of more than fifty atoms exists and that truth is contingent, but he does not make it true that it is possible that nothing composed of more 3To see the accounts that elicit this charge of extravagance, see Plantinga [1974] and Lewis [2001b, especially x1]. 4Lewis [2001b], especially x1.8. This isn’t the whole story for Lewis. The actual world and its parts make some modal truths true as well. The point here, though, is that Lewis needs unactual worlds and their parts in addition to the actual world and its parts. 5I say a strong incentive since each thinker claims that other benefits accrue from his preferred ontology. The Possibility Principle and Truthmakers for Modal Truths 3 than fifty atoms exists. I don’t think Armstrong does the boy’s work he sets out to do. And that may be because one really needs giants for it. 1. Armstrong’s Truthmakers for Truths of Possibility Truths of possibility can be distinguished into truths of possibility that are also truths of actuality and truths of mere possibility. A truth, p, is a truth of mere possibility if and only if }p is true and p is false (and, of course, the first sort of truth of possibility mentioned obtains if and only if }p and p are both true). Armstrong thinks that truths of mere possibility are the difficult truths of possibility to ground. For the other sort of truths—call them truths of actual possibility—Armstrong claims that the very thing that makes p true also makes }p true. To ground truths of mere possibility, he provides his Possibility principle. In Truth and Truthmakers, Armstrong offers the following argument for the Possibility principle. Suppose T makes p true. Suppose p is contingent (if it isn’t contingent, we aren’t talking about truths of mere possibility anymore). Given that p is contingent, it follows that it is possible that not-p. Armstrong claims (mistakenly, as we will see below) that since T makes p true, and p entails that it is possible that not-p, it seems that T should make it true that it is possible that not-p. Thus, if T makes p true and p is contingent, then T makes }*p true. ‘At a stroke’, says Armstrong, ‘we have removed the need for any truthmakers for truths of ‘‘mere possibility’’ except the truthmakers for contingent truths’ [2004: 84]. Armstrong formalizes his argument as follows, where the arrow stands for the cross-categorical necessitation that holds between truthmakers and truthbearers. Armstrong writes [loc. cit.]: 1. (T ! p) (assumed) 2. that p is contingent (assumed) 3. p entails that it is possible that not-p (from 2 and the nature of the contingency of propositions) Thus, 4.