The Evolution of Modern Metaphysics: Making Sense of Things (80 page)

David Lewis (1941–2001) was a student of Quine’s. As well as being an extraordinarily engaging thinker in his own right, he is also an especially interesting representative of post-Quinean analytic philosophy. On the one hand, he epitomizes the naturalistic spirit that has dominated analytic philosophy since the middle of the twentieth century and that Quine did so much to propagate. On the other hand, he epitomizes one of the most signal features of analytic philosophy’s more immediate past: a resurgence of
the kind of mainstream metaphysics that was practised in the early modern period; a resurgence, that is, of armchair reflection on such topics as substance, identity, necessity, causation, time, space, freedom, and the relation between mind and body.
²

Why ‘on the other hand’? Because the armchair reflection in question was an attempt, by the early moderns, to make sense of these things. Yet naturalism, even in its less extreme forms, is a revolt against any attempt to make sense of such things in other than a broadly scientific way.
³
Armchair reflection on the corresponding
concepts
(the concept of time, the concept of space, and so forth) is another matter. That may be naturalistically quite acceptable. But then it cannot, on a simple naturalistic conception, result in sense’s being made of the things themselves. True, Quine’s assault on the very idea of a dichotomy between reflection on a topic and reflection on the concepts associated with that topic has muddied the naturalistic waters. But not everyone in the analytic tradition has been persuaded by that assault. And certainly among those who have not, the thought that one can turn one’s philosophical gaze directly on, say, space, as opposed to the intellectual tools that people use to make sense of space, and then achieve insights into its character, rubs right against the naturalistic grain.

In some ways, if not in countless other ways, this situation is analogous to that which we witnessed in post-Kantian German philosophy. To develop the analogy in tandem with the cartoon sketch that I made at the beginning of
Chapter 11
: just as Kant modified Hume’s reaction to earlier metaphysical excesses, and created a system which allowed others, whether by purporting to follow him or by reacting against him, to indulge in metaphysics of the very sort that Hume might have thought he had exorcized, so too Quine modified the logical positivists’ reaction to earlier metaphysical excesses and created a system which has somehow allowed others to indulge in metaphysics of the very sort that the logical positivists might have thought they had exorcized, certainly of a sort that seems contrary to the naturalistic spirit that the logical positivists fostered and that has
itself survived this new-found interest in old-style metaphysics. One of my principal aims in the present chapter is to explain how this has happened, using Lewis as a paradigm case. And while it would be stretching things to say that Lewis plays Fichte or Hegel to Carnap’s and Quine’s Hume and Kant, I do believe that there are deep and important similarities between the story that I tried to tell at the end of
Part One
and the story that I have to tell here.

But first, I must mention one feature of the situation that makes my task especially difficult. I have in mind the curious (and in my view suspect
⁴
) lack of self-consciousness that accompanies this reversion to earlier metaphysical practices.
⁵
Recent work in analytic metaphysics has involved surprisingly little reflection on the nature of the enterprise.
⁶
This means that my story about what has been going on cannot be informed in any significant way by the practitioners’ own sense of what has been going on. Lewis is a case in point. His metaphysical work has countless laudable features. It is fertile, deep, beautifully crafted, and endlessly fascinating. But it is not particularly self-reflective. It is, in the terms of my Preface, very much work in metaphysics rather than meta-metaphysics. Since my own primary concern is with meta-metaphysics, what follows will therefore be highly selective in what it draws from that work.

2. Lewis’ Quinean Credentials; or, Lewis: Empiricist, Naturalist, Physicalist

Lewis is an empiricist. Or at least, he is an epistemic empiricist.
⁷
In his account of knowledge he equates basic evidence with ‘perceptual experience and memory’ (‘Knowledge’, p. 424) – although, just like Quine (see §3 of the previous chapter), he equates them non-dogmatically, the equation being, if correct, correct only because of contingent features of reality.

Lewis is also a naturalist. He is not perhaps an extreme Quinean naturalist, prepared to say that the scientific way to make sense of things is ‘the’ way to make sense of things. But he is enough of a naturalist to say that the
scientific way to make sense of things is the paradigmatic way to make sense of things; and that it stands in no need of any kind of Cartesian vindication from philosophy. He never does say this, in so many words. It is nevertheless clear that he would be totally unsympathetic to the Cartesian project. One thing that helps to make this clear is his attitude to a related project concerning mathematics, the project of ridding mathematics of that which is philosophically problematical. He writes:

That will not do. Mathematics is an established, going concern. Philosophy is as shaky as can be. To reject mathematics for philosophical reasons would be absurd. If we philosophers are sorely puzzled by the [entities] that constitute mathematical reality, that’s our problem. We shouldn’t expect mathematics to go away to make our life easier. (
Parts of Classes
, p. 58)
⁸

Another thing that helps to make clear the hostility with which Lewis would greet the Cartesian project is a Quinean account that he gives, if not of our scientific beliefs, then at least of our (scientifically informed) common-sense beliefs. He writes:

It is far beyond our power to weave a brand new fabric of adequate theory
ex nihilo
, so we must perforce preserve the one we’ve got. A worthwhile theory must be credible, and a credible theory must be conservative. It cannot gain, and it cannot deserve, credence if it disagrees with too much of what we thought before. And much of what we thought before was just common sense….

Common sense has no absolute authority in philosophy…. [But] theoretical conservatism is the only sensible policy for theorists of limited powers, who are duly modest about what they could accomplish after a fresh start. (
Plurality
, p.134)
⁹

I ascribe naturalism to Lewis, then, not because he anywhere explicitly commits himself to it, but because of how the naturalistic spirit that I mentioned in the previous section pervades his work and is manifest in what he does explicitly say about other, related matters.

Finally, Lewis is a physicalist. He states his physicalism as follows:

It is the task of physics to provide an inventory of all the fundamental properties and relations that occur in the world
¹⁰
…. We have no
a priori
guarantee of it, but we may reasonably think that present-day physics already goes a long way toward a complete and correct inventory…. And we may reasonably hope that future physics can finish the job in the same distinctive style…. [That is,] if we optimistically extrapolate the triumph of physics hitherto, we may provisionally accept that
all fundamental properties and relations that actually occur are physical. This is the thesis of [physicalism]. (‘Reduction’, p. 292)
¹¹

Lewis is an empiricist, a naturalist, and a physicalist, then. His Quinean credentials are impeccable. Later we shall see some significant differences between Quine and him. But these differences, I shall suggest, are altogether less significant and altogether less profound than the similarities. There is a continuity between the two thinkers that speaks volumes concerning the
Zeitgeist
within analytic philosophy to which I have already referred.

One very interesting and telling
difference
between them is as much temperamental as it is philosophical; it serves, in fact, to reinforce the impression of philosophical kinship. I have in mind the way in which Quine revels in the systematicity of his thinking, searching for ever more elegant and ever more economical ways of connecting the various elements of what I called in §1 of the previous chapter ‘his profound synoptic vision’.
¹²
Lewis, by contrast, tells us in the Introduction to his first volume of essays, ‘I should have liked to be a piecemeal, unsystematic philosopher, offering independent proposals on a variety of topics. It was not to be. I succumbed too often to the temptation to presuppose my views on one topic when writing on another’ (1st Introduction, p. ix).
¹³
A couple of pages later he lists what he calls ‘some recurring themes that unify the papers in this volume, thus
frustrating my hopes of philosophizing piecemeal’ (ibid., p. xi). Lewis is a systematist
malgré
lui
. It is almost as if the naturalistic spirit to which I have been referring, and which is one of the main sources of his systematicity, has taken possession of him.

That said, his aversion to system finds some sort of expression in the
content
of his overall vision, whereby ‘all there is to the world is a vast mosaic of local matters of particular fact, just one little thing and then another’ (2nd Introduction, p. ix). Lewis calls this thesis ‘Humean’, ‘in honor of the great denier of necessary connections’ (ibid.).
¹⁴
It leads him, for example, to endorse the Quinean view of physical objects mentioned in §6 of the previous chapter: the view that physical objects have temporal parts that are strictly distinct from one another, albeit united by various kinds of continuity, including, most notably, causal continuity (e.g.
Plurality
, pp. 204–206). It also has a curious echo – I put it no more strongly than that – in his work on what might fairly be described as the metaphysics of mathematics. Many philosophers of mathematics, and indeed many mathematicians, taking their lead largely from Frege, hold mathematics to be fundamentally about sets. But what exactly is a set? According to Cantor’s two famous definitions, a set is ‘any gathering into a whole … of distinct perceptual or mental objects’ (Cantor (
1955
), p. 85) or ‘a many that allows itself to be thought of as a one’ (Cantor (
1932
), p. 204).
¹⁵
Lewis complains that this account fails in the basic case of a singleton, that is to say a set with only one member, such as the set of English popes or the set of terrestrial moons. (Where is ‘the many’ in either of these cases?) In
Parts of Classes
he develops a rival account, whereby the case of a singleton really is the basic case and bigger sets are quite literally made up of singletons. Thus your singleton and my singleton together constitute our pair set, the set whose only two members we are. Each of them is literally a part of it. Sethood, on this conception, is not fundamentally a matter of manies begetting ones; it is fundamentally a matter of ones begetting different ones, which in turn beget yet different ones, and so on. Thereafter the different little begotten ones make up bigger ones. It is all markedly atomistic.

Before we turn our attention to what is undoubtedly the most notorious of Lewis’ metaphysical views, I want to mention one further respect in which he reveals his Quinean credentials. Although he shares Quine’s sense of the arbitrariness of some of our decisions concerning what to assert in metaphysics, or more generally concerning what to assert in philosophy,
¹⁶
he
is also resolutely Quinean in his insistence that they are decisions concerning
what to assert
, each objectively true or false as the case may be. Thus:

Once the menu of well-worked-out theories is before us, philosophy is a matter of opinion. Is that to say that there is no truth to be had? Or that the truth is of our own making, and different ones of us can make it differently? Not at all! If you say flatly that there is no god, and I say that there are countless gods …, then it may be that neither of us is making any mistake of method…. But one of us, at least, is making a mistake of fact. Which one is wrong depends on what there is. (1st Introduction, p. xi)
¹⁷

3. Modal Realism

Aptly, the notorious view to which I referred towards the end of the previous section is a view about what there is. Lewis dubs it
modal realism
(
Plurality
, p. 2). It is the view – a throwback to Leibniz – that, as well as the actual world and all that constitutes it, there are countless other possible worlds and all that constitutes them.
¹⁸

Lewis’ conception of possible worlds and his philosophical interest in them are quite different from Leibniz’. For both of them, however, there is a basic link between possible worlds and modal notions such as necessity, possibility, and contingency. What is necessarily the case is what is the case in all possible worlds; what is possibly the case is what is the case in at least one possible world; and what is contingently the case is what is the case in this world, the actual world, but not in all of them.