Prima facie, giving up on the explanationist defense for an inductive defense of IBE has two benefits. First, it does not face any threat of vicious circularity, which means that it bypasses Fine’s challenge.Footnote 3 Second, it promises to be dialectically useful against empiricists by virtue of using an inference rule that empiricists accept. I will review two inductive approaches, and two corresponding objections to them, which provide a good basis for evaluating the overall plausibility of inductive defenses of IBE.Footnote 4
The Galilean Strategy
The main proposal in the so called ‘Galilean Strategy’ by Kitcher (2001) is that we can test whether or not IBE has been successful in observational contexts, and then generalize that reliability to include unobservable contexts. Thus, the Galilean Strategy is a two-step argument that we may recreate in its generalised form:
IBE is reliable in observable contexts.
We have no good reason to suppose that it will stop being reliable in unobservable contexts.
IBE is reliable in unobservable contexts.
The first step needs to establish the reliability of IBE in observable contexts. To this end, Kitcher offers a rather plausible set of arguments of the following sort:
People find themselves in all sorts of everyday situations in which objects are temporarily inaccessible, or are inaccessible to only some of the parties. Detectives infer the identities of criminals by constructing predictively successful stories about the crime, bridge players make bold contracts by arriving at predictively successful views about the distribution of the cards, and in both instances the conclusions they reached can sometimes be verified subsequently. (Kitcher 2001, 176)
Kitcher’s suggestion is this: in observational contexts where objects are temporarily unobservable, we can entertain a host of theories, some of which will prove to be successful and others not. At some later time, when the same objects are no longer unobservable, one will find out which theories were true and, according to Kitcher, also find a strong correlation between success and truth. The core of the argument, then, is that:
[...] realists think that everyday experience supports a correlation between success and truth. They deny that empiricists can simply stipulate the limits of reliability of this correlation. (Kitcher 2001, 178)
Kitcher’s argument is inductive in so far as the reliability of the success-to-truth inference is premised on its past successes, whereby success can be confirmed by observation. The second step of the argument is that it is ‘metaphysical hubris’ to suppose that IBE’s limit of reliability should happen to correlate with the limits of human perception.
It is in the second step of the argument that things start to become vexed. Why, exactly, should the empiricist have to accept that the lack of a defeater for the continued reliability of IBE from observable to unobservable entities provides reason to believe that this reliability holds? As Magnus (2003) argues, the lack of such reasons is not enough to establish that such inferences are reliable regarding unobservables. Empiricists may simply remind Kitcher that no inductive evidence for the reliability of IBE with respect to the unobservable has been presented. While it might be true that there are no reasons to think that the reliability of IBE stops at the limit of human perception, there are no reasons to think that it continues either. The reliability of IBE with respect to unobservables cannot, on Kitcher’s account, be confirmed observationally.
Bird (2006) defends the legitimacy of explanatory inference in science by pointing to the fact that being an unobservable is a contingent fact. An inductive defense of IBE can exploit these contingencies to show that inferences to unobservables can be made, and later be confirmed observationally:
[Explanatory] inferences to the existence of unobservables have later been verified by direct observation once observational techniques have improved. We can now observe microbes and molecules, the existence of which was once a purely theoretical, explanatory hypothesis. (Bird 2006, 160)
The argument draws on the fact that technological progress has increased our epistemic boundaries so as to allow previously unobservable entities to become observable, suggesting that we can observationally confirm inferences to unobservables. Bird’s argument seems to contain precisely the element that was lacking in Kitcher’s—the success of IBE with respect to unobservables. To convince the empiricist, however, it too fares poorly. The cases clearly lack observational confirmation of the success of IBE with respect to the unobservable, even supposing that IBE is successful. Bird references successful inferences to microbes and molecules, but those are precisely the kind of entities that empiricists would say are unobservable. Such instances of IBE, while possibly successful, cannot be shown to be successful on empiricists terms.
The Problem with Inductive Defenses of IBE
It is now clear what the underlying problem of the inductive approach to defending IBE really is: the strategy of providing successful inferences to unobservables implies a failure of confirmation of that success by observation. The strategy of providing observational confirmation of successful inferences, in terms of observing the inferred objects or the conclusion of the inference, only works when objects are observables. We may think of the inductive defense as amounting to two claims:
Instances of IBE with respect to unobservables have been successful.
Confirmation of inferential success in such cases can be obtained by observation.
For the inductive defense to work against the empiricist, both (A) and (B) must be the case, since (A) is the claim that is defended, and (B) is the only dialectically viable route to defend (A). It is easy to see, however, that if (A) is satisfied then \(\lnot\) (B) must be the case. This is because whatever epistemology one may proceed with in order to satisfy (A), it could not possibly be (B) given an empiricist understanding of the epistemic salience of observability. Conversely, if (B) is satisfied then \(\lnot\) (A) must be the case. This is because the methodological assumption that (B) is satisfied leaves no possible route to satisfying (A). Again, this is due to the empiricist understanding of the unobservable/observable distinction. If we can confirm that inferences have been successful by observation, those inferences were made to observables. Any justification of such inferences does not extend to unobservables.
The very specific class of inferences that realists need to be reliable—inferences to unobservables—have conclusions that cannot be observationally confirmed. To argue for the general reliability of IBE, of which inferences to unobservables would be a subset, would run into two objections. The first objection is the empiricist classic rebuttal of sheep and lambs, which states that there is no reason for empiricists to venture beyond what the actual evidence, in this case successful inferences with respect to observables, shows. Even if some available epistemology shows that IBE is a generally reliable mode of reasoning, empiricists simply do not have to accept that this entails the reliability of IBE with respect to unobservables. It is entirely possible that the reliability of IBE is context-dependent and restricted to observables, and there is no evidence of the sort empiricists accept that can show that this possibility is false. The second objection, targeting Kitcher’s defense, is that a generalized defense of IBE would imply that metaphysicians using IBE in their theorizing would be as justified as scientific realists are. In other words, there would be no way to stop the metaphysical inflation of scientific realism, given that metaphysicians use IBE. If IBE is generally reliable, there is no reason why this reliability should not extend to metaphysics as well.Footnote 5 Between these two objections, a generalization of the reliability of IBE appears to be too costly a route to venture for realists.
We may now take stock of the defenses of IBE that I have considered. The explanationist defense was charged with vicious circularity because it uses IBE as a rule to justify the claim that IBE is justified. Even if Psillos and others have argued that this rule-circularity is not to be conflated with its viciously premise-circular cousin, the defense will ultimately suffer from dialectical issues. Perhaps such a strategy is effective against someone who is on the fence with respect to IBE, but anti-realists in general, and constructive empiricists in particular, are not. The inductive defense of IBE came in two different forms. Kitcher’s defense tried to establish the reliability of IBE by testing it in an observable environment, a move the consequences of which opponents would have to accept. Once this reliability could be established, the defense was supplemented with an argument claiming that since we have no reason to think that reliability of IBE correlates with observation, IBE is reliable with respect to the unobservable. Bird’s inductive defense claimed that we may observe the successes of IBE with respect to unobservables when observational technology enables us to catch up with our inferences. As we have seen, Bird’s defense neglects the empiricist’s epistemic divide between observable/unobservable and so cannot prove the alleged success of IBE with respect to unobservables without begging the question against the empiricist. Kitcher’s defense suffers from the inverse problem. He can prove the success of IBE, but only with respect to observables.
The empiricist distinction between observable and unobservable appears to be insurmountable for a dialectically successful defense of IBE. Any evidence for the reliability of IBE with respect to unobservables must somehow contain successful inferences to unobservables that can be observationally confirmed. A tall order, to say the least.