This book is a defense of modal realism; the thesis that our world is but one of a plurality of worlds, and that the individuals that inhabit our world are only a few out of all the inhabitants of all the worlds. Lewis argues that the philosophical utility of modal realism is a good reason for believing that it is true.

These works, as the sub-title makes clear, are unfinished sketches for Philosophical Investigations, possibly the most important and influential philosophical work of modern times. The 'Blue Book' is a set of notes dictated to Witgenstein's Cambridge students in 1933-1934: the 'Brown Book' was a draft for what eventually became the growth of the first part of Philosophical Investigations. This book reveals the germination and growth of the ideas which found their final expression in Witgenstein's later work. It is indispensable therefore (...) to students of Witgenstein's thought and to all those who wish to study at first-hand the mental processes of a thinker who fundamentally changed the course of modern philosophy. (shrink)

The principle of modal ubiquity - that every truth is necessary or contingent - and the validity of possibility introduction, are principles that any modal theory suffers for failing to accommodate. Advanced modal claims are modal claims about entities other than spatiotemporally unified individuals (perhaps, then, spatiotemporally disunified individuals, sets, numbers, properties, propositions and events). I show that genuine modal realism, as it has thus far been explicitly developed, and in so far as it deals with advanced modal claims, cannot (...) accommodate the principles in question. On behalf of the genuine modal realist I motivate and propose a redundancy interpretation of advanced possibility claims and extend that interpretation to the cognate cases of necessity, impossibility and contingency. I then show that the problematic principles as they apply to advanced modal claims can be derived from these interpretations. I show further how the proposed interpretation enables the genuine modal realist to deal with a number of objections that centre on the alleged inadequacy of the genuine modal realist's expressive resources. I conclude that genuine modal realism emerges the stronger for having been shown capable of dealing with advanced modal claims on the basis of no conceptual and ontological resources beyond those it requires to deal with ordinary modal claims. (shrink)

I find a lost wallet containing the owner's address and a lot of cash. Shall I keep it or return it? Suppose I have the ‘liberty of indifference’: whatever I do, I could have done otherwise. Indeed, part of what is meant in saying I act freely is that either way what I do is up to me. And let's allow this liberty requires that my choice is not a logical consequence of the past and natural laws. If I return (...) the wallet, I could have kept it without violating a law of nature or changing the past. Let's call this ‘situation S’ . Suppose I return the wallet.Others are also in S: free people find lost wallets every day. Each of us can freely return the wallet we find. It doesn’t follow immediately that we can all return it, however. That each ticket holder can win the lottery doesn’t entail they can all win it. We need the additional premiss that no number of people freely returning the wallet prevents the remainder from freely returning it. In short: each of us in S can freely return the wallet. Further, no number of us doing so prevents the remainder from doing so. Therefore it's possible that we all freely do what I do.According to Modal Realism , other possible worlds are concrete realities and the people in them as real as you and me. Some of these people are in S. Each of them can freely return the wallet; none of them is prevented from exercising that ability by others doing so, including others in worlds causally isolated from theirs. For instance, our doings in the actual world no more limit their abilities than …. (shrink)