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Unification beyond justification: a strategy for theory development

  • S.I. : Evidence Amalgamation in the Sciences
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This paper considers the importance of unification in the context of developing scientific theories. I argue that unifying hypotheses are not valuable simply because they are supported by multiple lines of evidence. Instead, they can be valuable because they guide experimental research in different domains in such a way that the results from those experiments inform the scope of the theory being developed. I support this characterization by appealing to the early development of quantum theory. I then draw some comparisons with discussions of robustness reasoning.

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  1. However, see Forster (2010) for an analysis in contemporary physics specifically using Whewell’s notion of consilience.

  2. Spohn (1994) has also discussed unification in relation to IBE and common cause.

  3. In recent talks, Janssen has characterized the force of a COI not as a legitimate inference to the truth of a theory, but as an indicator that an idea is worth pursuing.

  4. See Weisberg (2006), Trizio (2012), Nederbragt (2012), Kuorikoski and Marchionni (2016) and Schupbach (2016) for examples. Miyake (2015) discusses a related methodological technique of decomposition in the context of theory construction.

  5. See Kao (2015) for a reconstruction of such an argument.

  6. This refers to the spectrum of radiation emitted by an ideal body that perfectly absorbs, then re-emits all radiation incident upon it.

  7. See also Darrigol (1992) for useful discussions.

  8. The specific heat of a substance refers to the amount of heat required to raise a certain quantity of that substance by one degree Kelvin.

  9. Einstein used a different notation which was equivalent to expressing quantities in terms of h.

  10. The inconsistency arises from the two different ways Planck used to calculate the equilibrium entropy of a blackbody. The first assumes that the energy of the resonator takes on integral multiples of an undetermined amount \(\epsilon \). The other relies on a calculation using Maxwell’s theory of electricity, which are expressions of periodic functions that do not restrict their possible values to discrete ones.

  11. See Norton (2006) for a reconstruction of the reasoning.

  12. See Heilbron and Kuhn (1969) for a detailed treatment of this episode.

  13. See Kao (2015) for discussion of this idea.

  14. “Nous ferons, par suite, l’hypothèse suivante. Les propriétés générales de toutes les molécules ou atomes qui déterminent les phénomènes de rayonnement ne consistent pas dans l’intervention d’éléments particuliers d’énergie, mais en ceci, que la manière dont se produisent les échanges d’énergie dans un temps plus ou moins long est dominée par une loi universelle” (Sommerfeld 1912, p. 314).

  15. See Schickore and Coko (2013) for an overview and further references.

  16. She also provides a thorough argument decoupling unification from both truth and explanation.


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Correspondence to Molly Kao.

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I am grateful for the valuable feedback I received from the audience members at the workshop on Exploring Scientific Method at the Munich Center for Mathematical Philosophy in May 2017, as well as the annual 2017 conference of the Canadian Philosophical Association. I would also like to thank Michel Janssen and two anonymous referees for their helpful comments.

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Kao, M. Unification beyond justification: a strategy for theory development. Synthese 196, 3263–3278 (2019).

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