MCMULLIN CLAIMS ON BEHALF OF RETRODUCTION
Those claims I introduced briefly above; let me quote the entire passage now:
retroduction is not an atemporal application of rule as deduction is. It is extended in time, and logically very complex. It is properly inference, since 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 cause of a (partially) expressed sort.
The language here is, of course, that of scientific realism. It is because the cause is, in some sense however qualified, affirmed as real cause, that retroduction functions as a distinct form of inference. (184)
McMullin goes on to indicate clearly the position in epistemology that provides the epistemic side of this scientific realism:
It is a far cry from the demonstrations of Aristotle to the retroductions of modern theoretical science. Where they differ is, first, that retroduction makes no claim of necessity, and it settles for less, much less, than definitive truth. It can, under favorable conditions, when theories are well-established, yield practical certainty. (185)
What we see here, I think, is that by “inference” McMullin means something more than something that “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 cause of a (partially) expressed sort” (184). Even adding, for example, “rationally” after the word “move” would not be enough to complete what he means. Logically speaking, there is still a gap between the statement that this is a rational sort of move from evidence to an affirmed conclusion and the claim that this sort of move is “truth-conducive,” that it is likely to lead to true conclusions. When McMullin speaks here of a degree of confidence, and of practical certainty, he is surely not just describing a subjective state of mind of the person engaged in retroduction. He is claiming that retroductive inference, to the unobserved causes of observed events classified as effects, leads to truth.