Technically van Fraassen’s target is scientific realism, which can be thought of as an extension of structural realism depending on how broad we construe the domain of science. His arguments against scientific realism are compelling precisely because he gives a kind of weak characterisation of the scientific enterprise. Such an enterprise is often (he argues) assumed falsely to be accurately characterised as follows31:
Science aims to give us, in its theories, a literally true story of what the world is like; and acceptance of a scientific theory involves the belief that it is true.
On such a characterisation we see science as a fallible enterprise aiming to achieve the truth, where a minimal condition for the truth of a theory is that its acceptance induces belief in that theory. We take this to be a fair characterisation. A consequence of this view is that science can be seen to accept the existence of unobservable entities, or relations where such things feature in the claims of an accepted scientific theory, and then by definition we are expected to believe in the existence of these entities and relations. Van Fraassen objects to the latter conclusion; belief, he thinks, is not necessitated by acceptance of the theory. He is motivated by broadly empiricist leanings, whereby all those things unobservable in nature are open to disbelief.32 In a very strong
sense, seeing is believing for the constructive empiricist. As such, the adequacy of a scientific theory is to be tested only on the action and behaviour of the observable entities that fall under the remit of the theory. However it’s not clear as to whether an unobservable element of one theory will forever remain unobservable given the march of technology. This prompts the following (very general) constructivist account of the scientific enterprise:
Science aims to give us theories which are empirically adequate; and acceptance of a theory involves as belief only that it is empirically adequate.33
This latter constraint on belief allows us to incorporate a theory within our beliefs in so far as its acceptance lends itself to some practical application - however this is construed. In such a way van Fraassen can argue for the adoption of a particular theory of causation for its predictive benefits, and so there seems no bar for him to adopt the best scientific theories whatever their initial motivation so long as he can find some ultimate use for the theories. In effect scientific theories are accepted to be fundamentally underdetermined. However there seems to be a continuum here in terms of the degree to which a theory is useful or practical. So with such a pragmatic motivation we might worry that the underdetermination of a theory’s truth can be extended to the question over whether a theory is empirically adequate? Surely grue-type cases emerge here too, if there no restraint on rational acceptance other than empirical adequacy and empirical adequacy is purely a pragmatic measure? The natural objection here is to insist that empirical adequacy is a measure determined by the objective correctness of a theory with respect to the actions of its observable parameters.
31
[32]pg8
32I’m showing my hand here. Strictly speaking the constructivist need not tolerate the suggestion that anything
unobservable, properly speaking, exists.
To present a theory is to specify a family of structures, its models; and secondly, to specify certain parts of those models (theempirical substructures) as candidates for the direct representation of observable phenomena.34
A theory is defined asempirically adequate just when some model of the theory can be put in isomorphism with the observable facts, i.e. when the empirical substructures of the model reflect all the observable facts. Note, it is not true to say that a theory is empirically adequate just when all empirical substructures of said model can be put into an isomorphism with some of the facts. Putting all this together, we see that theory acceptance is to be mandated by empirical adequacy on pain of the obvious underdetermination problems for liberal pragmatism. The more observable facts reflected in the theory the better the theory. With this in mind, we now turn to the arguments against scientific realism.
IBE does not entail Realism
A cheap construal of abductive reasoning might appear to offer the suggestion that the success of scientific theorising is apt to induce belief in the existence of the entities (observable or unobserv- able) postulated in the theory. However, this is not totally accurate. We can, with van Fraassen, be voluntarists about beliefs - whereby IBE may appear in the canons of rational inference along with the probabilistic axioms but in no way does the acceptance of these axioms necessitate their usage, or belief in their consequences. So for instance we might see that our mouse trap has been activated, the cheese has disappeared and remain adamant that no mouse exists behind the wall even though IBE would suggest the contrary. This argument is sound. However, it is uncompelling since presumably we still seek to answer the existence question which prompted the argument. The empirical fact that people can be seen to ignore inference to the best explanation, does nothing to undermine the realist thesis. The argument does show that realism is not the only contender in this debate...we could also be inexplicably agnostic, or suggest reasons to doubt the existence of mice.
A better argument against the realist position is deployed by van Fraassen to indicate that realism necessitates an explanatory regress. The idea is used to undermine the power of IBE. He writes...
...even if we were to grant the correctness (or worthiness) of the rule of inference to the best explanation, the realist needs some further premise for his argument [in each case of IBE]... So the realist will need his special extra premiss that every universal regularity in nature needs an explanation, before the rule will make realists of us all.35
This argument would seem to seriously problematise the idea that realism follows by appeal to IBE. But it is not at all evident that the realist’s search for explanation is so fevered. Indeed we might think that belief in the existence of a realist theory which appears to explain some phenomena is motivated precisely because it explains said phenomena (without beingad hoc), not because we feel some inordinate need to find or introduce novel explanatory theories at each instance. Van Fraassen’s argument targets the philosophical use of IBE to motivate realism wholesale, but realism is always properly motivated piecemeal. Nevertheless van Fraassen’s argument is correct as far as it goes, which is not very far.36
34 [32]pg64 35
[32]pg21
36
More forcefully, we could make the argument that the structure of a theory is all we can come to know, either in the sense that it is all we can come to cogently communicate or perceive. For details on this species of argument see [34]
Theory Laden Observation
The insistence that all scientific claims are theory laden is often taken to be a point against realism of any stripe. But it’s easy to concede that there is some truth to the observation without troubling the realist thesis. Although our language might well incorporate various theoretical predicates, most such predicates have been well motivated before their widespread inclusion in our scientific theories. As for the notion that the concept of observability is theory laden - van Fraassen accepts the charge that even if the limits of observability are determined by community consensus, then so be it, “it is, on the face of it, not irrational to commit oneself only to a search for theories that are empirically adequate, ones whose models fit the observable phenomena, while recognising that what counts as observable phenomenon is a function of what the epistemic community [insists]”.37 But by similar reasoning it is not irrational to commit ourselves to a search for causal (supervenience, grounding...etc) explanations while recognising that the criteria of adequacy on such searches is fundamentally determined by community consensus. In short, the charge that our account of dependency based explanation is riddled with theory-laden vocabulary cuts both ways, and is not obviously worrying in either case. A cogent objection to structural realism must further demonstrate that our theory incorporates a harmful theoretical hangover from our model of e.g. causal dependency, in which case we enter into debate over how to assess the adequacy or harmful nature of our assumptions. Such a discussion is nothing more than a debate over model preference, so at worst such a discussion only improves our model.
Structural Realism is not the only route to Success
You might want to challenge the constructivist on the basis that they seem to collapse the line between useful and correct theories. While the realist can explain dependency relations between particular events by appeal to deep structure, the constructivist appears prone to denying that there is an unobservable factual structure of dependence. Instead he allows for only definitional or correlative connections based on a history of observation. Again, this realist argument falters because it begs the question we are trying to determine. If truth is a mark of success then the ability to account for presumed true relations of dependence will always make the realist theory more successful than the constructivist theory. By equating explanatory power with the ability to identify unobservable structure, then we deny that there is any explanatory power to be derived from statistical information of observed correlation between events. This is false. The success of a theory may be measured in practical terms without question-begging appeal to supposed truth- approximation of our hypothetical deep structure.
In the same vein we might think that since scientific explanations of the properties of objects are often based on the hypothesised unobservable microstructures, the constructivist would be at a loss to develop analogous but strictly empirical explanations for the same phenomena. However, van Fraassen can argue that a difference in microstructures will have observable consequences, hence given enough time and data the constructivist will be able to infer from the statistical correlation some serviceable property of the entity in question to facilitate predictions. This property can be fed into all predictive (or otherwise scientific) uses of this entity in our theory so that wherever the realist supplies an explanation so too the may the constructivist given enough effort. Worse news for the realist is that the microstructure hypothesis allows for the development of an indeterminate number of alternative theories with subtly different assumptions about the microstructure of the world. This effectively makes any choice of microstructure a result of some “hidden variable” which determines the choice. Such a “hidden variable” must be made explicit if it is to be rendered reasonable. By making such assumptions explicit we can see science as a history of competing narratives where each narrative “suggests new statements of observable regularities and...corrects old ones”38
37
[32]pg19
The Ultimate Argument does not ensure Realism
The final argument for realism is dubbed the ultimate argument by van Fraassen who clearly wants to draw attention to the misnomer. The idea, initially propounded by Putnam is to argue that the success of our theories, the accuracy of their terms, their predictive power, etc are all rendered miraculous if our theories are in fact false but simply empirically adequate. The challenge is to say that there must be an empirically adequate reason for why we converge on empirically adequate theories. Putnam suggest that the actual truth of the theory is the best candidate reason. Although, given the picture of the scientific enterprise which van Fraassen has developed you might predict his answer:
The Darwinist says: Do not ask why themouse runs from its enemy. Species which did not cope with their natural enemies no longer exist. That is why there are only ones who do. In the same way, I claim that the success of current scientific theories is no miracle... For any scientific theory is born into a life of fierce competition, a jungle red in tooth and claw. Only the successful theories survive - the ones whichin fact latched on to the actual regularities in nature.39
As such, he argues we should expect that our arrival at the acceptance of an empirically ade- quate theory is well motivated and not accidental. So construed we have a plausible constructivist view of the scientific enterprise. Hence allowing van Fraassen’s construal of scientific activity we come to the primary empiricist conclusion: “the assertion of empirical adequacy is a great deal weaker than the assertion of truth, and the restraint to acceptance delivers us from metaphysics” Hence it appears that our efforts in the previous chapter were improperly motivated.