Revisability in Mathematics

The Contingency Postulate of Truth. - Is there a statement that cannot be false under any contingent conditions? Two well-known philosophical schools have given contradictory answers to this question about the existence of a necessarily true statement: Fallibilists (Albert, Keuth) have denied its existence, transcendental pragmatists (Apel, Kuhlmann) and objective idealists (Wandschneider, Hösle) have affirmed it. Dieter Wandschneider has (following Vittorio Hösle) translated the principle of fallibilism, according to which every statement is fallible, into a thesis which he calls the (...) contingency postulate of truth (CPT). It says: <For every true statement there are contingent conditions.> If this postulate were true, it would mark an insurmountable boundary of knowledge: a final epistemic justification would then not be possible. Wandschneider has therefore developed a counterargument to show that the contingency postulate of truth cannot be formulated without contradiction and implies the thesis that there is at least one necessarily true statement. This essay deals with the systematic question whether the contingency postulate of truth really cannot be presented without contradiction. To this end I will first present the contingency postulate and the associated problems (I.). Then I will analyze Wandschneider's argument against the consistency of the contingency postulate (II.) and finally reject it with the help of some considerations from the field of epistemic logic (III.). (shrink)

Quine's holistic empiricist account of scientific inquiry can be characterized by three constitutive principles: *noncontradiction*, *universal revisability* and *pragmatic ordering*. We show that these constitutive principles cannot be regarded as statements within a holistic empiricist's scientific theory of the world. This claim is a corollary of our refutation of Katz's [1998, 2002] argument that holistic empiricism suffers from what he calls the Revisability Paradox. According to Katz, Quine's empiricism is incoherent because its constitutive principles cannot themselves be rationally revised. Using (...) Gärdenfors and Makinson's logic of belief revision based on epistemic entrenchment, we argue that Katz wrongly assumes that the constitutive principles are *statements* within a holistic empiricist's theory of the world. Instead, we show that constitutive principles are best seen as *properties* of a holistic empiricist's theory of scientific inquiry and we submit that, without Katz's mistaken assumption, the paradox cannot be formulated. We argue that our perspective on the status of constitutive principles is perfectly in line with Quinean orthodoxy. In conclusion, we compare our findings with van Fraassen's [2002] argument that we should think of empiricism as a stance, rather than as a doctrine. (shrink)

This paper discusses an intriguing, though rather overlooked case of normative disagreement in the history of philosophy of mathematics: Weyl's criticism of Dedekind’s famous principle that "In science, what is provable ought not to be believed without proof." This criticism, as I see it, challenges not only a logicist norm of belief in mathematics, but also a realist view about whether there is a fact of the matter as to what norms of belief are correct.

The present paper aims at showing that there are times when set theoretical knowledge increases in a non-cumulative way. In other words, what we call ‘set theory’ is not one theory which grows by simple addition of a theorem after the other, but a finite sequence of theories T1, ..., Tn in which Ti+1, for 1 ≤ i < n, supersedes Ti. This thesis has a great philosophical significance because it implies that there is a sense in which mathematical theories, (...) like the theories belonging to the empirical sciences, are fallible and that, consequently, mathematical knowledge has a quasi-empirical nature. The way I have chosen to provide evidence in favour of the correctness of the main thesis of this article consists in arguing that Cantor–Zermelo set theory is a Lakatosian Mathematical Research Programme (MRP). (shrink)