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?????The first objection has as a premise that it is part of the meaning of "explanation" that if one theory is more explanatory than another, the former must be more informative than the latter (see, e.g., van Fraassen 1983, Sect. 2). The alleged problem then is that it is "an elementary logical point that a more informative theory cannot be more likely to be true [and thus] attempts to describe inductive or evidential support through features that require information (such as 'Inference to the Best Explanation') must either contradict themselves or equivocate" (van Fraassen 1989, 192).Nevertheless, the said community might justify its use of IWE by dint of the following reasoning: "Scientific theories tend to be hugely unsuccessful. These theories were arrived at by application of IWE. That IWE is a reliable rule of inference--that is, a rule of inference mostly leading from true premises to true conclusions--is surely the worst explanation of the fact that our theories are so unsuccessful. Hence, by application of IWE, we may conclude that IWE is a reliable rule of inference."(It is to be noted that Lombrozo's experiments are directly concerned with some proposals that have been made for explicating abduction in a Bayesian framework; see Section 4.) However, the most pertinent remarks about the normative status of abduction are so far to be found in the philosophical literature.(See Koehler 1991, for a survey of some of these studies; see also Brem and Rips 2000.) More telling still, Lombrozo (2007) shows that, in some situations, people tend to grossly overrate the probability of simpler explanations compared to more complicated ones.3.1 Criticisms We have already encountered the so-called argument of the bad lot, which, we saw, is valid as a criticism of ABD1 but powerless against various (what we called) congruous rules of abduction.The Status of Abduction Even if it is true that we routinely rely on abductive reasoning, it may still be asked whether this practice is rational.While this would be an utterly absurd conclusion, the argument leading up to it cannot be convicted of being viciously circular anymore than Boyd's argument for the reliability of abduction can (if Psillos is right).Although these studies are not directly concerned with abduction in any of the forms discussed so far, they nevertheless suggest that taking into account explanatory considerations in one's reasoning may not always be for the better.This section discusses the main criticisms that have been levelled against abduction, as well as the strongest arguments that have been given in its defense.The first even purports to challenge the core idea underlying abduction; the second is not quite as general, but it is still meant to undermine a broad class of candidate explications of abduction.The elementary logical point is supposed to be "most [obvious] ... in the paradigm case in which one theory is an extension of another: clearly the extension has more ways of being false" (van Fraassen 1985, 280). It is important to note, however, that in any other kind of case than the "paradigm" one, the putative elementary point is not obvious at all.For instance, experimental studies have shown that when people are able to think of an explanation for some possible event, they tend to overestimate the likelihood that this event will actually occur.It is fair to note that for Psillos, the fact that a rule-circular argument does not guarantee a positive conclusion about the rule at issue is not sufficient for such an argument to be valid.Both objections are due to Bas van Fraassen.We may safely assume that the use of this rule mostly would lead to the adoption of very unsuccessful theories.It would appear, then, that there must be something else amiss with rule-circularity.We here consider two objections that are meant to be more general.3.

تلخيص
3. The Status of Abduction
Even if it is true that we routinely rely on abductive reasoning, it may still be asked whether this practice is rational. For instance, experimental studies have shown that when people are able to think of an explanation for some possible event, they tend to overestimate the likelihood that this event will actually occur. (See Koehler 1991, for a survey of some of these studies; see also Brem and Rips 2000.) More telling still, Lombrozo (2007) shows that, in some situations, people tend to grossly overrate the probability of simpler explanations compared to more complicated ones. Although these studies are not directly concerned with abduction in any of the forms discussed so far, they nevertheless suggest that taking into account explanatory considerations in one’s reasoning may not always be for the better. (It is to be noted that Lombrozo’s experiments are directly concerned with some proposals that have been made for explicating abduction in a Bayesian framework; see Section 4.) However, the most pertinent remarks about the normative status of abduction are so far to be found in the philosophical literature. This section discusses the main criticisms that have been levelled against abduction, as well as the strongest arguments that have been given in its defense.

3.1 Criticisms
We have already encountered the so-called argument of the bad lot, which, we saw, is valid as a criticism of ABD1 but powerless against various (what we called) congruous rules of abduction. We here consider two objections that are meant to be more general. The first even purports to challenge the core idea underlying abduction; the second is not quite as general, but it is still meant to undermine a broad class of candidate explications of abduction. Both objections are due to Bas van Fraassen.

The first objection has as a premise that it is part of the meaning of “explanation” that if one theory is more explanatory than another, the former must be more informative than the latter (see, e.g., van Fraassen 1983, Sect. 2). The alleged problem then is that it is “an elementary logical point that a more informative theory cannot be more likely to be true [and thus] attempts to describe inductive or evidential support through features that require information (such as ‘Inference to the Best Explanation’) must either contradict themselves or equivocate” (van Fraassen 1989, 192). The elementary logical point is supposed to be “most [obvious] … in the paradigm case in which one theory is an extension of another: clearly the extension has more ways of being false” (van Fraassen 1985, 280).

It is important to note, however, that in any other kind of case than the “paradigm” one, the putative elementary point is not obvious at all. For instance, it is entirely unclear in what sense Special Relativity Theory “has more ways of being false” than Lorentz’s version of the æther theory, given that they make the same predictions. And yet the former is generally regarded as being superior, qua explanation, to the latter. (If van Fraassen were to object that the former is not really more informative than the latter, or at any rate not more informative in the appropriate sense—whatever that is—then we should certainly refuse to grant the premise that in order to be more explanatory a theory must be more informative.)

The second objection, proffered in van Fraassen 1989 (Ch. 6), is levelled at probabilistic versions of abduction. The objection is that such rules must either amount to Bayes’ rule, and thus be redundant, or be at variance with it but then, on the grounds of Lewis’ dynamic Dutch book argument (as reported in Teller 1973), be probabilistically incoherent, meaning that they may lead one to assess as fair a number of bets which together ensure a financial loss, come what may; and, van Fraassen argues, it would be irrational to follow a rule that has this feature.

However, this objection fares no better than the first. For one thing, as Patrick Maher (1992) and Brian Skyrms (1993) have pointed out, a loss in one respect may be outweighed by a benefit in another. It might be, for instance, that some probabilistic version of abduction does much better, at least in our world, than Bayes’ rule, in that, on average, it approaches the truth faster in the sense that it is faster in assigning a high probability (understood as probability above a certain threshold value) to the true hypothesis (see Douven 2013 and Douven and Wenmackers forthcoming; see Climenhaga forthcoming for discussion). If it does, then following that rule instead of Bayes’ rule may have advantages which perhaps are not so readily expressed in terms of money yet which should arguably be taken into account when deciding which rule to go by. It is, in short, not so clear whether following a probabilistically incoherent rule must be irrational.

For another thing, Douven (1999) argues that the question of whether a probabilistic rule is coherent is not one that can be settled independently of considering which other epistemic and decision-theoretic rules are deployed along with it; coherence should be understood as a property of packages of both epistemic and decision-theoretic rules, not of epistemic rules (such as probabilistic rules for belief change) in isolation. In the same paper, a coherent package of rules is described which includes a probabilistic version of abduction. (See Kvanvig 1994, Harman 1997, Leplin 1997, Niiniluoto 1999, and Okasha 2000, for different responses to van Fraassen’s critique of probabilistic versions of abduction.)

3.2 Defenses
Hardly anyone nowadays would want to subscribe to a conception of truth that posits a necessary connection between explanatory force and truth—for instance, because it stipulates explanatory superiority to be necessary for truth. As a result, a priori defenses of abduction seem out of the question. Indeed, all defenses that have been given so far are of an empirical nature in that they appeal to data that supposedly support the claim that (in some form) abduction is a reliable rule of inference.

The best-known argument of this sort was developed by Richard Boyd in the 1980s (see Boyd 1981, 1984, 1985). It starts by underlining the theory-dependency of scientific methodology, which comprises methods for designing experiments, for assessing data, for choosing between rival hypotheses, and so on. For instance, in considering possible confounding factors from which an experimental setup has to be shielded, scientists draw heavily on already accepted theories. The argument next calls attention to the apparent reliability of this methodology, which, after all, has yielded, and continues to yield, impressively accurate theories. In particular, by relying on this methodology, scientists have for some time now been able to find ever more instrumentally adequate theories. Boyd then argues that the reliability of scientific methodology is best explained by assuming that the theories on which it relies are at least approximately true. From this and from the fact that these theories were mostly arrived at by abductive reasoning, he concludes that abduction must be a reliable rule of inference.

Critics have accused this argument of being circular. Specifically, it has been said that the argument rests on a premise—that scientific methodology is informed by approximately true background theories—which in turn rests on an inference to the best explanation for its plausibility. And the reliability of this type of inference is precisely what is at stake. (See, for instance, Laudan 1981 and Fine 1984.)

To this, Stathis Psillos (1999, Ch. 4) has responded by invoking a distinction credited to Richard Braithwaite, to wit, the distinction between premise-circularity and rule-circularity. An argument is premise-circular if its conclusion is amongst its premises. A rule-circular argument, by contrast, is an argument of which the conclusion asserts something about an inferential rule that is used in the very same argument. As Psillos urges, Boyd’s argument is rule-circular, but not premise-circular, and rule-circular arguments, Psillos contends, need not be viciously circular (even though a premise-circular argument is always viciously circular). To be more precise, in his view, an argument for the reliability of a given rule R that essentially relies on R as an inferential principle is not vicious, provided that the use of R does not guarantee a positive conclusion about R’s reliability. Psillos claims that in Boyd’s argument, this proviso is met. For while Boyd concludes that the background theories on which scientific methodology relies are approximately true on the basis of an abductive step, the use of abduction itself does not guarantee the truth of his conclusion. After all, granting the use of abduction does nothing to ensure that the best explanation of the success of scientific methodology is the approximate truth of the relevant background theories. Thus, Psillos concludes, Boyd’s argument still stands.

Even if the use of abduction in Boyd’s argument might have led to the conclusion that abduction is not reliable, one may still have worries about the argument’s being rule-circular. For suppose that some scientific community relied not on abduction but on a rule that we may dub “Inference to the Worst Explanation” (IWE), a rule that sanctions inferring to the worst explanation of the available data. We may safely assume that the use of this rule mostly would lead to the adoption of very unsuccessful theories. Nevertheless, the said community might justify its use of IWE by dint of the following reasoning: “Scientific theories tend to be hugely unsuccessful. These theories were arrived at by application of IWE. That IWE is a reliable rule of inference—that is, a rule of inference mostly leading from true premises to true conclusions—is surely the worst explanation of the fact that our theories are so unsuccessful. Hence, by application of IWE, we may conclude that IWE is a reliable rule of inference.” While this would be an utterly absurd conclusion, the argument leading up to it cannot be convicted of being viciously circular anymore than Boyd’s argument for the reliability of abduction can (if Psillos is right). It would appear, then, that there must be something else amiss with rule-circularity.

It is fair to note that for Psillos, the fact that a rule-circular argument does not guarantee a positive conclusion about the rule at issue is not sufficient for such an argument to be valid. A further necessary condition is “that one should not have reason to doubt the reliability of the rule—that there is nothing currently available which can make one distrust the rule” (Psillos 1999, 85). And there is plenty of reason to doubt the reliability of IWE; in fact, the above argument supposes that it is unreliable. Two questions arise, however. First, why should we accept the additional condition? Second, do we really have no reason to doubt the reliability of abduction? Certainly some of the abductive inferences we make lead us to accept falsehoods. How many falsehoods may we accept on the basis of abduction before we can legitimately begin to distrust this rule? No clear answers have been given to these questions.

Be this as it may, even if rule-circularity is neither vicious nor otherwise problematic, one may still wonder how Boyd’s argument is to convert a critic of abduction, given that it relies on abduction. But Psillos makes it clear that the point of philosophical argumentation is not always, and in any case need not be, to convince an opponent of one’s position. Sometimes the point is, more modestly, to assure or reassure oneself that the position one endorses, or is tempted to endorse, is correct. In the case at hand, we need not think of Boyd’s argument as an attempt to convince the opponent of abduction of its reliability. Rather, it may be thought of as justifying the rule from within the perspective of someone who is already sympathetic towards abduction; see Psillos 1999 (89).

There have also been attempts to argue for abduction in a more straightforward fashion, to wit, via enumerative induction. The common idea of these attempts is that every newly recorded successful application of abduction—like the discovery of Neptune, whose existence had been postulated on explanatory grounds (see Section 1.2)—adds further support to the hypothesis that abduction is a reliable rule of inference, in the way in which every newly observed black raven adds some support to the hypothesis that all ravens are black. Because it does not involve abductive reasoning, this type of argument is more likely to also appeal to disbelievers in abduction. See Harré 1986, 1988, Bird 1998 (160), Kitcher 2001, and Douven 2002 for suggestions along these lines.