As is to be expected it is the epistemological form of the Thesis which is most directly amenable to evaluation. Not only that, as matters stand it is, as noted, unarguably false for any reasonable interpretation of physics. Recall:
ECT2: A science X is complete iff X is capable of fixing the likelihood of X-type outcomes solely by reference to X-type entities, powers, states, laws, etc.
Physics as it stands is manifestly incapable of delivering the required goods. It does not form an integrated body of knowledge, and as well as not being integrated contains, if taken as a whole, various areas of
51
In a discussion of causal closure principles Kim (1998: 40) describes the key consideration as whether in the course of tracing the causal ancestry of a physical event, it will be necessary to ‘crossing the boundary between the physical and nonphysical’. My concern here is with how far down the line can be pushed while still preserving completeness.
52 Feigl (1953: 384) admits the difficulty of giving a non-arbitrary criterion for distinguishing physical from non-physical laws, and proposes that a ‘more definite meaning may be suggested by formulating the thesis of physicalism in the following way: The set of physical laws which enables us to deduce the facts of chemistry will be sufficient for biology and psychology.’
53
Although I make reference to such evidence in a number of places in what follows, including Chapter Two (especially section 7).
conflict and inconsistency.54 Even if we were to assume with heroic optimism that all of these problems could be dealt with by means of the proverbial ‘large enough sheet of paper and sharp enough pencil’ approach, the thus integrated body of theory would not be complete in the required sense, for the simple reason that there are all manner of unresolved problems and empirical questions in physics at all scales and with respect to all phenomena.55 To assume that these can all be answered by physics in the end is partly to beg the question, and also, perhaps inevitably, to create a need for an even larger piece of paper and a vastly sharper pencil to deal once again with the consistency problem.
The epistemological version of the Thesis would be on its ideal ground in the event that the world was best described by some deterministic theory. Persistent scepticism aside, being in a position to predict actual outcomes with the accuracy made possible by a true deterministic theory would be just about the best available kind of confirmation. Determinism is less straightforward and simple than classical modern thinkers, and the architects of rational mechanics, such as Laplace, tended to think, though. John Earman (1986) has discussed the ways in which even classical mechanics is not deterministic in the ways traditionally expected, and various other considerations indicate that even the behaviour of some deterministic systems may well be impossible to predict (e.g. Lorenz 1963).
Failures of epistemological completeness do not in general indicate any automatic difficulty for ontological completeness though. This is, in fact, one of the principal theses defended in what follows. As the case of non-linear dynamics shows, even deterministic systems may be genuinely unpredictable. More generally, any direct inference from failures of prediction to failures of ontological causal closure would be a
non sequitur. Alleged counterexamples are always subject to reinterpretation.56 And even without a successful predictive theory we might well have good grounds for believing in physical causal closure, in the event that we could defend the claim that the only kinds of causal process there was any reason to believe operated in some given system were physical ones. Let us look, then, at the ontological form of the Thesis:
OCT2: A domain of reality X is complete iff X occurrences always have sufficient X-type causal ancestries.
In this case it is clear that where the domain X in question is the physical, it would suffice for the falsehood of the ontological Completeness Thesis if there was any well substantiated evidence that there was some class of physical occurrences which either did not have sufficient physical causal ancestries, or the
54 These theoretical difficulties vary from the well-known issue of the apparent conflict between general relativity and quantum mechanics, to wider problems about the relationships between any fundamental law and the phenomenological laws relevant to particular phenomena. Cartwright’s criticism of fundamental laws (1980, 1983) is discussed in Chapter Four below.
55
The difficulties here vary considerably too, from cases of hypothesised but either undiscovered or contested particles to questions about the large-scale structure of space-time.
sufficient causal ancestries of which did have a non-physical component. What might lead us to think that such a state of affairs obtained?
For a start it is important to note that the mere availability of some causal claim which relates a physical outcome to a non-physical antecedent, for example ‘my wanting caused my walking’ will not by itself be decisive. More generally any claim so relating a physical effect with a non-physical cause will be unproblematic from the point of view of the Completeness Thesis just as long as it is still possible to defend the claim that there is a sufficient physical cause as well. Given two such claims there are a range of possible responses including, inter alia, accepting the overdetermination or rejecting it and arguing for some kind of identity thesis.57 It is not my intention here to get into those questions, though, simply to focus on the question of completeness. And what is needed to create difficulties for the Completeness Thesis is reason to believe that there is not a sufficient physical ancestry for some physical outcome.
There are various ways in which this might occur. Dualistic interactionism is one, any of a number of forms of causal emergence involving ‘downwards causation’ another. The matter of fact in all cases is the same, though, and that is this: if any of these views is true, there will be some physical outcomes which just do not have sufficient physical causal ancestries, however those ancestries are to be understood.
The ontological form of the Completeness Thesis could turn out to be not so much false as utterly unacceptable. What I mean by this is that rather than evidence for positive failures of completeness, it might turn out that there were reasons to think that the very notion of a well defined domain of the physical was incoherent, or at least that our best evidence indicated that there was no such domain to be found at the actual world. This is one way of thinking of the force of Cartwright’s assault on traditional confidence in high level theoretical laws of physics, a view she dubs fundamentalism. I postpone treatment of that view to the fourth chapter of this work, and in the interim focus more directly on views which suggest that the Completeness Thesis is false.