In McMullin’s description of retroductive inference as the process by which science arrives at theories, we encounter a great liberalization of traditional epistemology’s view of the sciences. As McMullin moves to his conclusion, he shows us how much had to be progressively discarded. First, the Aristotelian tradition’s pretension that we can arrive at contingent empirical truths with certainty. Then on the other side the classical empiricist’s claim that the general truths about nature can be deduced from the phenomena, or arrived at by a straight induction from the evidence. Going even further, scrutinizing his own heroes of epistemology, McMullin takes his distance from William Whewell and Charles Sanders Peirce. The kind of confidence in this sort of inference, expressed by Whewell (1847, vol. 2, 67, 284, 286) with his proud claim that consilience is the mark of truth, and that no truly consilient theory has ever been found false, McMullin eschews.

But McMullin is equally adamant that the kind of rule-following paradigm of such lively contemporaneous movements as formal

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epistemology is wide off the mark. Retroductive inference is a creative, innovative, often conceptually revolutionary, risk-taking, at the same time severely self-policing, epistemic enterprise.

All of this must be music to any would-be empiricist’s ears today. The emphasis on choice and practical decision in scientific progress that entered early on in Hans Reichenbach’s, Rudolf Carnap’s, and other logical empiricists’ writings, are here just as much evident in McMullin’s scientific realist epistemology. So what sets McMullin still clearly opposite to that tradition?

I think we can see the clues first of all in McMullin’s brief reference to the first great schism he notes in the history he is retelling:

Looking at the Middle Ages as a whole, one would obviously have to separate two quite diverse methodological traditions, the Aristotelion and the nominalist [ . . . .] The Aristotelians remained faithful on the whole, to the ideal of demonstration set down in the Posterior Analytics, while developing some aspects of that doctrine, the distinction between demonstrations propter quid and quia, for example, much more fully than Aristotle had done. The nominalists began to shape the notion of inductive generalization, entirely rejecting the notion of necessary connection between essence and property on which the older notion of demonstration had been based. (Inference, 154)

That nominalist turn was also the first step on a course leading to Hume’s critique of a concept of causality involving any sort of necessary connections in nature.

There is no countering McMullin’s critique in The Inference That Makes Science of Bacon, Hume, Mill and other such figures in the history of the empiricist tradition who tried to raise naı̈ve inductive methods to the status of scientific methodology. But that critique, however well it does in demolishing those attempts, does not end the story for a more radical empiricist view of our epistemic situation. McMullin sets those mistakes aside only to return to the tradition that assures us of epistemic safety, of a proper handling of evidence that we can be assured will be likely to lead to truth about nature’s deepest structure.

We cannot be entirely sure, from McMullin’s actual text, what all is involved in this. I think we can be sure that the “likely” does not signify mere subjective probability on the side of the scientist, or for that matter, the scientific realist. In addition, we have McMullin’s own qualifying comment quoted above: “likelihood (in the everyday sense of that term, not the sense given it in probability theory)” (McMullin 2007, 176). Whatever that sense may be, it is to be understood as involving sufficient objectivity to give bite to the professed realism. The entire tradition recounted by McMullin, including the classical empiricism and the inductivism he associates with it, consists in the unfolding of an ever more desperate search for epistemic safety. If not demonstration then induction, if not evidence from recondite experimental or observational procedures then the sense data of immediate

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perception, if not inductive generalization from such data then retroductive inference to the vera causa . . . safety for our beliefs about the natural world can be gained.

So in this respect McMullin and the sorts of epistemology that he submits to his severe critique are the same. The real opposition emerges in a rival strand never given such ample critical attention: the vision of our epistemic situation perhaps most clearly found in Blaise Pascal, but always initially evoked in the recurring empiricist reactions to realism, before the temptation to seek safety defeats it again.

That other reaction, the one that I would think proper to what empiricism can be today, is to set aside any such illusory safety (see also van Fraassen 2002). Recall that McMullin characterized retroduction as “properly inference” because it “enables one to move in thought from the observation of an effect to the affirmation, with greater or lesser degree of confidence, of the action of a (partially) expressed sort.” From this, we can glean a concept of inference in general, as a practice enabling one to move in thought from given or assumed information to a conclusion. There are applicable criteria of rationality, to ensure that at least consistency, perhaps some stronger standard of coherence, even plausibility, are preserved. But what they can guarantee only is to avoid inevitable or necessary failure to reach truth. There is in the satisfaction of such criteria no guarantee, however much we would like to have one, of reaching truth, with anything more than subjective certainty or probability.

The real rival to McMullin’s vision is not the classical empiricist program of induction as objective road from certainty in the deliverances of sense to certainty going beyond the concrete individual fact. That was certainly a philosophical illusion; McMullin is right about that. When McMullin states, in “A Case for Scientific Realism,” that the success of retroductive inference is a contingent matter, he realizes a crucial point, but does not go far enough. That the contingent conditions for the success of retroduction actually obtain could only be inferred by retroductive inference: an insight that sweeps the rug from under any assurance of epistemic safety to be found there.

Rationality and criteria of rationality for our epistemic life will rule out self-sabotage, reject any procedures with built-in failure. Apart from that, there remains just the admission that our procedures will work for us, and give us the wherewithal to live and act in this world, only if the world continues to be hospitable to them—and the hope, or faith, that it shall be so.


1. I am personally as well as academically deeply indebted to Ernan McMullin from whom I learned much over the years; and I treasure especially the copy of The Inference That Makes Science that Ernan gave me.

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