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Charles Sanders Peirce introduced the logic of what he called “abduction” — a complement to both deduction and induction — with this example:
The surprising fact, C, is observed;
But if A were true, C would be a matter of course,
Hence, there is reason to suspect that A is true.
At least since Harry Frankfurt in 1958, many readers have been skeptical. Can’t we make up an infinite number of premises that could explain any surprising fact?
For instance, Kamala Harris has gained in the polls compared to Joe Biden. If it were true that voters generally prefer female presidential candidates, then her rise would be a “matter of course.” But it is a mistake to infer that Harris has gained because she is a woman. Other explanations are possible and, indeed, more plausible.
Note that “voters prefer women candidates” is an empirical generalization. Generalizations cannot be derived from any single case. If that is what abduction means, then it seems shaky. Its only role might be to suggest hypotheses that should then be tested with representative samples or controlled experiments.
But what if A (the premise) is not an empirical generalization but rather a model? For instance, a model might posit that Harris’ current position in the polls is the combined result of eight different factors, some of them general (voters usually follow partisan cues) and some of them quite unrepeatable (the incumbent president has suddenly bowed out).
Positing a model to explain a single case has risks of its own. Perhaps we add no insight by contriving an elaborate model just to fit the observed reality. And we might be tempted to treat the various components of the model as general patterns and apply them elsewhere, even though one case should give us no basis for generalizing.
But let’s look at this example from a different perspective–a pragmatic one, as Peirce would recommend. After all, Peirce calls his topic “Abductive Judgment” (Peirce 1903), suggesting a connection to practical reason or phronesis.
The question is what should (someone) do? For instance, a month ago, should Joe Biden have dropped out and endorsed Harris? Right now, should Harris accentuate her gender or try to balance it with a male vice-presidential candidate?
Inductive logic might offer some insights. Research suggests that the choice of vice-president has never affected the outcome of a presidential election, and this general inference would suggest that Harris needn’t pay attention to the gender of her VP. But induction cannot answer other key questions, such as what to do when you replace the nominee 100 days before the election. (There is no data on this matter because it hasn’t happened before.)
Besides, various factors can interrelate. The general pattern that vice-presidents do not matter might be reversed in a situation where the nominee had herself been the second person on the ticket until last week.
And the important questions are inescapably normative. For Harris, one good goal is to win the election, but she must attend to other values as well. For instance, I think she should adopt positions that would benefit working-class voters of all races. Possibly this would help her win by restoring some of Biden’s working-class coalition from 2020. Polling data would help us assess that claim. But I favor a worker-oriented strategy for reasons of justice, and I think the important question is how (not whether) to campaign that way.
Models of social phenomena typically incorporate descriptive elements (Harris is down by two points today), causal claims (Trump is still benefitting from a minor convention bump), and normative premises (Harris must win)–all combined for the purpose of guiding action.
Arguably, we cannot do better than abduction when we are trying to decide what to do next. Beginning with a surprising fact, C (and almost anything can be seen as “surprising”), we must come up with something, A, that we can rely on to guide our next steps. A should not be a single sentence, but rather a model composed of various elements.
It is worthwhile to consider evidence from other cases that may validate or challenge components of A. But it is not possible to prove or disprove A. As the pioneering statistician Georg Rasch said, “Models should not be true, but it is important that they are applicable, and whether they are applicable for any given purpose must of course be investigated. This also means that a model is never accepted finally, only on trial.”
If a model cannot be true, why should we make it explicit? It lays out what we are assuming so that we can test the assumptions as we act. It promotes learning from error. And it can help us to hold decision-makers accountable. When evaluating leaders, we should not assess the outcomes, which are beyond anyone’s control, but rather the quality of their models and their ability to adjust in in the light of new experience.
Sources: Peirce, C.S. 1903. Lectures on Pragmatism, Lecture 1: Pragmatism: The Normative Sciences; Frankfurt, Harry G. “Peirce’s notion of abduction.” The Journal of Philosophy 55.14 (1958): 593-597. See also: choosing models that illuminate issues–on the logic of abduction in the social sciences and policy; modeling social reality; different kinds of social models