We argue that, under the usual assumptions for sufficiently strong arithmetical theories that are subject to Gödel’s First Incompleteness Theorem, one cannot, without impropriety, talk about *the* Gödel sentence of the theory. The reason is that, without violating the requirements of Gödel’s theorem, there could be a true sentence and a false one each of which is provably equivalent to its own unprovability in the theory if the theory is unsound.
I make a point concerning the construction ‘A or B or both’ in English, to the effect that if the connective ‘or’ is understood exclusively across the board then this familiar construction cannot convey the intended inclusive sense of disjunction. If we take ‘or’ inclusively, ‘A or B or both’ has the function of emphasizing that the disjunction is inclusive; taking ‘or’ exclusively, it does nothing.
We take an argument of Gödel's from his ground‐breaking 1931 paper, generalize it, and examine its validity. The argument in question is this: "the sentence G says about itself that it is not provable, and G is indeed not provable; therefore, G is true".
We demonstrate that, in itself and in the absence of extra premises, the following argument scheme is fallacious: The sentence A says about itself that it has a property F, and A does in fact have the property F; therefore A is true. We then examine an argument of this form in the informal introduction of Gödel’s classic (1931) and examine some auxiliary premises which might have been at work in that context. Philosophically significant as it may be, that particular (...) informal argument plays no rôle in Gödel’s technical results. Going deeper into the issue and investigating truth conditions of Gödelian sentences (i.e., those sentences which are provably equivalent to their own unprovability) will provide us with insights regarding the philosophical debate on the truth of Gödelian sentences of systems—a debate which goes back to Dummett (1963). (shrink)
I aim at dissolving Kripke's dogmatism paradox by arguing that, with respect to any particular proposition p which is known by a subject A, it is not irrational for A to ignore all evidence against p. Along the way, I offer a definition of 'A is dogmatic with respect to p', and make a distinction between an objective and a subjective sense of 'should' in the statement 'A should ignore all the evidence against p'. For the most part, I deal (...) with Kripke's original version of the paradox, wherein the subject wishes, above all else, to avoid losing her true belief or gaining a false one; in the final section I investigate the possibility of having a paradox for a subject who values knowledge above anything else. (shrink)
Essentialism about natural kinds involves talking about kinds across possible worlds. I argue that there is a non-trivial transworld identity problem here, which cannot be (dis)solved in the same way that Kripke treats the corresponding transworld identity problem for individuals. -/- I will briefly discuss some ideas for a solution. The upshot is scepticism concerning natural-kind essentialism.
ABSTRACT: Appealing to the failure of counterfactual support is a standard device in refuting a Humean view on laws of nature: some true generalisations do not support relevant counterfactuals; therefore not every true general fact is a law of nature—so goes the refutation. I will argue that this strategy does not work, for our understanding of the truth-value of any counterfactual is grounded in our understanding of the lawhood of some statements related to it.
In several publications, Juliet Floyd and Hilary Putnam have argued that the so-called ‘notorious paragraph’ of the Remarks on the Foundations of Mathematics contains a valuable philosophical insight about Gödel’s informal proof of the first incompleteness theorem – in a nutshell, the idea they attribute to Wittgenstein is that if the Gödel sentence of a system is refutable, then, because of the resulting ω-inconsistency of the system, we should give up the translation of Gödel’s sentence by the English sentence “I (...) am unprovable”.I will argue against Floyd and Putnam’s use of the idea, and I will indirectly question its attribution to Wittgenstein. First, I will point out that the idea is inefficient in the context of the first incompleteness theorem because there is an explicit assumption of soundness in Gödel’s informal discussion of that theorem. Secondly, I will argue that of he who makes the observation that Floyd and Putnam think Wittgenstein has made about the first theorem, one will expect to see an analogous observation about Gödel’s second incompleteness theorem – yet we see nothing to that effect in Wittgenstein’s remarks. Incidentally, that never-made remark on the import of the second theorem is of genuine logical significance.. (shrink)
With the aim of providing an empiricist-friendly rational reconstruction of scientists’ modal talk, I represent and defend the following unoriginal idea of relative modalities, focused on natural ones: the assertion of physical necessity of φ can be understood as the logical provability of φ from the background theory of the context of assertion. I elaborate on my conception of the background theory, and reply to a number of objections, among which an objection concerning the failure of factivity.