Tarik Tijanovic

When David Lewis put forward modal realism—the view that all possible worlds are concrete—he neglected the explanatory dimension of such a model of existence. In this paper my goal is to put modal realism in the context of the principle of sufficient reason (PSR) and consider the explanatory structure of a modal realist model of existence. I consider two modal realisms—the platonist and the theistic modal realism. According to the former, the explanans for the existence of all possible worlds is the principle of plenitude according to which all possible worlds must exist. According to the latter, the explanans for the existence of all worlds is God. The two modal realisms converge in the fact that the explanans for any existing particular fact is constituted by the entire logical space. This is the main place where modal realisms governed by the PSR diverge from traditional necessitarian systems in which the explanans for any particular facts is constituted only by its own world. Also, the point of divergence between the two modal realisms is twofold. First, the platonist version doesn’t admit God in its existence. Second, it allows for what “brute facts” which in the end are not brute given that they have explanation in terms of the principle of plenitude.

Peter Van Inwagen argues that The Principle of Sufficient Reason (PSR) either leads to contradiction or it leads to necessitarianism. Although I agree with Van Inwagen that the relationship between the PSR and necessitarianism is close, I argue that the PSR is compatible with innocent versions of necessitarianism. In this project my main argument is that modal realism can account for the PSR and integrate it within an innocent version of necessitarianism. My main claim will be that each fact in each possible world is grounded in the principle of plenitude. Also, while each fact is grounded in plenitude, it avoids rigid necessitarianism because (i) actuality is not captured by the PSR, (ii) things could be otherwise because there are other worlds, and due to the principle of recombination (iii) cardinality of possible worlds is maximized and (iv) there are no necessary connections between distinct individuals. As a result, the relationship between modal realism and the PSR is symbiotic. Through modal realism, the PSR also results as: having its scope extended to the realm of all possibilia rather than being confined to mere actuality; it solves indeterminacy problems like Leibniz’s problem of space or the hard problem of consciousness; it accounts for facts in lawless worlds etc. On the other hand, through the PSR, modal realism gets one more benefit in its inventory because it accounts for the PSR. Thus, modal realism still continues on Lewis’ paradoxical path of proving to be highly pragmatic but counterintuitive at the same time. If added benefits are worth the costs for modal realism is still an open question.