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Discovery without a ‘logic’ would be a miracle

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Abstract

Scientists routinely solve the problem of supplementing one’s store of variables with new theoretical posits that can explain the previously inexplicable. The banality of success at this task obscures a remarkable fact. Generating hypotheses that contain novel variables and accurately project over a limited amount of additional data is so difficult—the space of possibilities so vast—that succeeding through guesswork is overwhelmingly unlikely despite a very large number of attempts. And yet scientists do generate hypotheses of this sort in very few tries. I argue that this poses a dilemma: either the long history of scientific success is a miracle, or there exists at least one method or algorithm for generating novel hypotheses with at least limited projectibility on the basis of what’s available to the scientist at a time, namely a set of observations, the history of past conjectures, and some prior theoretical commitments. In other words, either ordinary scientific success is miraculous or there exists a logic of discovery at the heart of actual scientific method.

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Notes

  1. It is often ambiguous whether the stages are supposed to be temporal or logical. See, e.g., (Hoyningen-Huene 2006).

  2. This is actually one of three characterizations Curd considers. He deems this the least plausible of the three.

  3. An interesting exception is work by philosophers on procedures for generating mechanistic hypotheses in the life sciences (Darden 2002; Craver and Darden 2013).

  4. That isn’t quite fair if one understands abduction in Peirce’s sense. Peirce took ‘guessing’, the inception of a new idea, to be a stage of abduction (Tschaepe 2014). However, he seems to have thought that guessing is not rationally analyzable. Those who have touted abduction as the logic of ‘discovery’ (e.g., (Hanson 1961)) often ignore the actual stage of guessing, or assume a trivial mechanism of generation, as in King et al. (2004).

  5. According to Savary (1995), this felicitous phrase was coined by Gutting (1980).

  6. Kelly (1987) actually refers to such a method as a “generation procedure” and reserves the singular term “the logic of discovery” to refer to the study of all such procedures. My references to a logic of discovery are equivalent to Kelly’s talk of “a generation procedure.”

  7. My use of this term is a slightly unfaithful replication of Kelly’s (1987).

  8. Note that Laudan considers only the confirmationist subset of consequentialist approaches to theory justification. Falsificationist theories are thus ruled out of consideration.

  9. The insistence on a recursively enumerable suitability relation can be dropped. It turns out that “[f]or any nonempty degree of uncomputability, there are infinitely many suitability relations...properly of that degree for which there is a strongly adequate hypothesis generation machine”(Kelly 1987, p. 449).

  10. Curiously, these models seem to be the only ones to garner significant attention amongst philosophers of science, e.g., (Gillies 1996).

  11. Note that any path through such a tree is equivalent to some sentence in disjunctive normal form.

  12. Using ‘kernel methods’ that essentially apply a nonlinear transformation to the feature space to get a new space that is linearly separable.

  13. The naive Bayes classifier is also one of the oldest (Maron and Kuhns 1960).

  14. Obviously, neither Hempel nor Laudan could have been aware of all of the methods reviewed here when they framed their objections, as many are recent inventions. But enough—such as decision trees, naive Bayes classifiers, and (for Laudan at least) the BACON lineage of heuristic search algorithms—were around by the time they penned their objections.

  15. Two of the most prominent are the mixture of Gaussians and independent component analysis (ICA) algorithms.

    Fig. 2
    figure 2

    a A representation of a naive Bayes model as a directed graph. b A hierarchical naive Bayes (HNB) model with a single layer of latent variables

  16. Let S be a set. A \(\sigma \)-algebra is a non-empty set \(\varSigma \) such that: (1) S is in \(\varSigma \), (2) if A is in \(\varSigma \) then so is the complement of A, and (3) the union of any sequence of elements of \(\varSigma \) is in \(\varSigma \). A measure is a function from \(\varSigma \) to the positive real numbers such that the null set maps to zero and such that the measure of the union of any finite or countably infinite set of disjoint members of \(\varSigma \) is equal to the sum of the measures of each set alone

  17. In a minority of cases, the definition of a variable (not substantive knowledge of its possible values) ensures that the space of logically possible values it can assume is bounded. For example, celestial longitude can only take on values between 0 and 360 degrees. In those cases, the argument of this section does not go through; there will be some finite, nonzero probability of guessing a new value correctly. I stress, however, that most physical variables take on an unbounded range of possible values.

  18. For technical reasons, it’s easier to consider left closed, right open intervals. The claims made in the text presume intervals of this sort.

  19. For various sorts of anti-realist, this is a plausible assumption, since hypotheses are individuated by their empirical consequences. Thus, each prediction counts for one hypothesis. The realist, however, individuates hypotheses based on what they say concerning observable and unobservable entities. In that case, I have perhaps made a dubious assumption. But no more can be said unless we know something about how to define the set of possible hypotheses and what to treat as equal regions of hypotheses.

  20. There is no probability measure obeying the Kolmogorov axioms of probability that is uniform over the entire real line. But one can assign a measure over the real line and ask about the relative size of subsets of the reals with respect to that measure.

  21. I do not intend to concede this point. As Penrose (1994) points out, we can represent and reason about uncomputable functions. To say there is nothing worth calling a logic of discovery given an uncomputable function that otherwise has all of the features of such a logic requires an argument. Presumably, such an argument would turn on the claim that to count as a logic of discovery, it must be possible to consciously implement the procedure, and that this can only be done for computable functions. Whatever we do that’s uncomputable, it is not and cannot be conscious, hence the talk about happy guesses and strokes of genius.

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Acknowledgments

I am grateful to Richard Burian, Lydia Patton, Tristram McPherson, Kelly Trogdon, Ted Parent, Gregory Novak, Daniel Kraemer, Nathan Rockford, Nathan Adams, and two anonymous reviewers for their insightful criticisms of earlier versions of this paper.

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Correspondence to Benjamin C. Jantzen.

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Jantzen, B.C. Discovery without a ‘logic’ would be a miracle. Synthese 193, 3209–3238 (2016). https://doi.org/10.1007/s11229-015-0926-7

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