Notes
It is true that, as an anonymous referee pointed out, very few mathematicians would be able to state the “relevant axioms.” This points to a divergence between this characterization of proof with actual mathematical proofs, whose starting points are subject-specific acceptable starting points, rather than (foundational) axioms. Still, mathematicians do generally acknowledge that such “relevant axioms” could be in principle made explicit – that is why this characterization will do for this context. The more so because, as it will be clear shortly, we won’t focus on disagreement concerning axioms.
It is not entirely clear what “perfect rigor” is, and even less clear whether that has been attained (Burgess and De Toffoli 2022; Paseau 2016). Remember that, of course, many of the proofs that were deemed to be rigorous at the time of Poincaré’s writing, would not be acceptable nowadays. Nevertheless, it is important that still at the time, an ideal of rigorous proof was shared by many mathematical communities. We will return on this issue later.
See, for example, (Maddy 2011).
Arguably, however, some of the axioms of set theory “force themselves upon us as true” (Gödel 1964, 271).
Indeed, foundational disagreement can also concern the choice of a logic.
See (Paseau 2015). Note that, notwithstanding the (missleading) name, probabilistic proofs are not genuine (deductive) proofs at all.
This is the “surveyability” requirement for proofs (Tymoczko 1979).
For instance, De Toffoli (2023) argues that in some cases diagrams are essential to the proof in which they figure. That is, that there are plausible criteria of identity for proofs such that when eliminating the diagrams from certain diagrammatic proofs we would inevitably transform such proofs into different ones.
This type of disagreement can also be seen to be linked to CONCEPTION OF PROOF-DISAGREEMENT. According to Wagner (2022, 5) the “problem of consensus [over the correctness of putative proofs] and individuation of proof are intertwined.” However, for the scope of this argument, we prefer to keep them separate.
Thanks to Fenner Tanswell for encouraging us to think of this case as a hybrid type of disagreement.
See (De Toffoli 2022, 256) for an analysis of this case from an epistemological perspective.
Note that the correctness of this reaction is accepted even from those epistemologists who advocate that in general one should stick to one’s own original position in face of disagreement (Kelly 2010, 199).
This is, however, not always the case. Vladimir Voevodsky, long before finding a mistake in his own results that granted him the Fields medal, was made aware of a counterexample. He wrongly believed that his results were in good standing and that the putative counterexample came from a fallacious argument (Voevodsky 2014).
In order for this process of self-correction to be possible, mathematical arguments must be shareable among practitioners, see (De Toffoli 2021a).
See (Goldstein 2013) discussing the ubiquity of PP-DISAGREEMENT in 17th century mathematics.
See (Brigaglia and Ciliberto 1998, 300).
Our translation from Italian.
This is not, according at least to Severi and Enriques, incompatible with mathematical rigor. Indeed, both mathematicians identified two types of rigor, one connected with the possibility of always adding more details and another, consisting in describing the mathematical facts faithfully. For a discussion, see (De Toffoli and Fontanari 2022).
They discuss a related result, the Theorem of Completeness of the Characteristic Series. The Fundamental Theorem under discussion is one of the main consequences of such Completeness Theorem.
Our translation from Italian.
This letter is stored in the Beniamino Segre Archives at the California Institute of Technology and reproduced (and partially translated) by Babbitt and Goodstein (2011).
Note that the situation might change radically due to technological innovations related to new computer proof assistants. These tools are making the formalization of mathematics more and more manageable (Avigad 2018).
These and related questions are addressed in (Burgess and De Toffoli 2022).
This definition is taken from the governmental website: https://www.usa.gov/federal-agencies/u-s-courts-of-appeal.
We report them here briefly, but the interested reader should consult (Wagner 2022).
See (Avigad 2021).
For a pluralist conception of rigor, see (Tanswell forthcoming).
There are important critiques to this view. Here are two objections that we find most relevant: (i) not all formal systems will do (a silly example of what won’t do is an inconsistent system), (ii) the overgeneration problem discussed in (Tanswell 2015): to a single p-proof, many formal proofs can be associated.
Note that this view is inspired by Burgess’s, but departs from his view in this respect.
For a discussion of these two types of rigor and their connection with different notions of objectivity in mathematics, see (De Toffoli and Fontanari 2022).
The distinction between rigor and acceptability for p-proofs parallels Miranda Fricker’s (1998) distinction between indicator properties and working indicator properties for good informants, which she develops in her investigation of the phenomenon of epistemic injustice. According to Fricker, a good informant is both competent and trustworthy – this is what constitutes rational authority. The indicator properties are properties that reliably indicate rational authority. Instead, working indicator properties “are those properties actually used in a given practice to indicate rational authority, and which may or may not be so reliable” (ibid. 168).
For a contemporary case, one might point to symplectic geometry (Hartnett 2017).
One such exception being Fesenko (2019).
This is related to the problem of how we should identify proofs, which is related to CONCEPTION OF PROOF-DISAGREEMENT. See Footnote 8. Thanks to one of the anonymous referees for this clarification.
We do not want to imply there is not but simply that our view does not entail there is one.
See (Fallis 2003).
Our translation from Italian.
See (Ciliberto and Sallent Del Colombo 2018, 15).
Our translation from Italian.
Our translation from Italian.
Our translation from Italian.
Our translation from Italian.
Our translation from Italian.
These can be numbered among “mathematical virtues” (Aberdein et al. 2021)
Our translation from Italian.
It was then fixed by Andrew Wiles in about one year with the help of his former student Richard Taylor.
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Acknowledgements
We wish to thank the two anonymous referees for their detailed comments that helped us clarify our positions. Thanks are also due to Fenner Tanswell for insightful suggestions. A recent draft was discussed during a reading group at IUSS Pavia – we are particularly grateful to Andrea Sereni and Guido Tana for their feedback. This research project was partially supported by GNSAGA of INdAM and by PRIN 2017 “Moduli Theory and Birational Classification.”
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De Toffoli, S., Fontanari, C. Recalcitrant Disagreement in Mathematics: An “Endless and Depressing Controversy” in the History of Italian Algebraic Geometry. glob. Philosophy 33, 38 (2023). https://doi.org/10.1007/s10516-023-09691-1
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DOI: https://doi.org/10.1007/s10516-023-09691-1