Confirmational Strategy 1
The first strategy (S1) looks for encouraging and discouraging posits in the theory T. Here one valuable resource lies in the discovery of apparent problems for T, usually by opponents who subject T's central tenets and auxiliary assumptions to hostile probing, hoping to expose those tenets as either wrong or superfluous.
Consider, for example, the ingenious efforts in the 1810s by defenders of the corpuscular theory to show that the central ideas of Fresnel's wave theory were wrong. Those efforts reached a peak in the episode leading to the experimental demonstration of the so-called “Poisson Spot,” a prediction Poisson and other corpuscularians thought was to be the ruin Fresnel's theory—to their surprise it crowned it. In a parallel set of battles, the supporters of T struggle to revise its auxiliary assumptions upon encountering difficulties in the theory's application. This kind of effort was apparent, for instance, when Thomas Young's discovery of double-slit interference in 1801 forced corpuscularians into convoluted auxiliary hypotheses to account for the phenomenon. Corpuscularians failed to convince, leading to the effective collapse of the particle camp.Study of how these animated investigations play out in a theory's course can help a realist make a preliminary selection of theory-parts that seem either crucial or not for the theory's empirical success. Two lists, drawn from multiple applications of this confirmational strategy, can be developed at this stage: List (L+), made of parts implicated in cases of impressive predictive success; and (L-), made of parts found implicated in unfulfilled predictions.
Once these two lists are preliminarily drawn up, the next realist task is to assess the impact on T's empirical progressiveness of each of the items listed. This assessment can be done for each part by evaluating the effect of removing it from T while keeping the others. The proposal is to recognize as (a) probably “crucial” to T's success only those parts in L+ whose removal clearly leads to T's stagnation, judging from T's overall track record, and (b) “suspect” those parts in L— whose removal clearly improves T's predictive power and/or frees T from seemingly intractable conceptual conundrums. In Fresnel's theory, for example, the yield of impressive predictions plummets if one removes certain posits (e.g. the transversal character of the light wave and the abstract spatial structure given by Fresnel's equations).
How well does this strategy help realism? The historical record of manifest retentions across theory-change seems good for L+ parts. Good but not without blemish, for it would have left in place the ether of light, at least throughout the 19th century (Cordero 2011). Strategy S1 helps realists but more is needed.
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