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Conditionals in Closed Set Logic

Over the last couple of days on Twitter, I was involved in a thread, kicked off by Dan Piponi, discussing closed set logic—the natural dual of intuitionistic logic in which the law of the excluded middle holds but the law of non-contradiction fails, and which has models in the closed sets of any topological space, as opposed to the open sets, which model intuitionistic logic. ¶ \(\def\ydash{\succ}\)This logic also has a nice sequent calculus in which sequents have one premise (or zero) and multiple conclusions. In the thread I made the claim that this is a natural and beautiful sequent calculus (it is!) but that the structure of the sequents means that the logic doesn’t have a natural conditional. The dual to the conditional (subtraction) can be defined, for which \(A\ydash B\lor C\) if and only if \(A-B\ydash C\). But the traditional conditional rules don’t work so well. ¶ I realised, when I thought about it a bit more, that this fact is something I’ve just believed for the last 20 years or so, but I’ve never seen written down, so now is as good as a time, and here is as good as a place as any to explain what I mean. ¶ ¶ Consider the conditional rules in the classical sequent calculus. They look something like this (give or take variations in the presentation, all equivalent given the classical structural rules): Classical sequent rules for the conditional. ¶ If we restrict these rules to multiple conclusion single... -

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Accommodation, Inference, Generics and Pejoratives

Abstract: In this talk, I aim to give an account of norms governing our uses of generic judgements (like “kangaroos have long tails”, “birds lay eggs”, or “logic talks are boring”), norms governing inference, and the relationship between generics and inference. This connection goes some way to explain why generics exhibit some very strange behaviour: Why is it, for example, that “birds lay eggs” seems true, while “birds are female” seems false, despite the fact that only female birds lay eggs? ¶ Given the connection between generics and inference, I’ll go on to consider how inference relates to the process of accommodation, which plays a significant role in how we manage dialogue and conversation. This, in turn, helps shed some light on some different... -

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Accommodation, Inference, Generics and Pejoratives

Abstract: In this talk, I aim to give an account of norms governing our uses of generic judgements (like “kangaroos have long tails”, “birds lay eggs”, or “logic talks are boring”), norms governing inference, and the relationship between generics and inference. This connection goes some way to explain why... -

Read More @ Consequently.org
Accommodation, Inference, Generics and Pejoratives

Abstract: In this talk, I aim to give an account of norms governing our uses of generic judgements (like “kangaroos have long tails”, “birds lay eggs”, or “logic talks are boring”), norms governing inference, and the relationship between generics and inference. This connection goes some way to explain why... -

Read More @ Consequently.org

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Accommodation, Inference, Generics and Pejoratives Abstract: In this talk, I aim to give an account of norms governing our uses of generic judgements (like “kangaroos have long tails”, “birds lay eggs”, or “logic talks are boring”), norms governing inference, and the relationship between generics and inference. This connection goes some way to explain why generics exhibit some very strange behaviour: Why is it, for example, that “birds lay eggs” seems true, while “birds are female” seems false, despite the fact... Consequently.org -


Accommodation, Inference, Generics and Pejoratives Abstract: In this talk, I aim to give an account of norms governing our uses of generic judgements (like “kangaroos have long tails”, “birds lay eggs”, or “logic talks are boring”), norms governing inference, and the relationship between generics and inference. This connection goes some way to explain why generics exhibit some very strange behaviour: Why is it, for example, that “birds lay eggs” seems true, while “birds are female” seems false, despite the fact... Consequently.org -


Defining Rules, Proofs and Counterexamples Abstract: In this talk, I will present an account of defining rules, with the aim of explaining these rules they play a central role in analytic proofs. Along the way, I’ll explain how Kreisel’s squeezing argument helps us understand the connection between an informal notion of validity and the notions formalised in our accounts of proofs and models, and the relationship between proof-theoretic and model- theoretic analyses of logical consequence. This is a talk for... Consequently.org -


What Proofs are For Abstract: In this short talk, I present a new account of the nature of proof, with the aim of explaining how proof could actually play the role in reasoning that it does, and answering some long-standing puzzles about the nature of proof. Along the way, I’ll explain how Kreisel’s Squeezing argument helps us understand the connection between an informal notion of of validity and the notions formalised in our accounts of proofs and models, and... Consequently.org -


Truth Tellers in Bradwardine's Theory of Truth Stephen Read’s work on Bradwardine’s theory of truth is some of the most exciting work on truth and insolubilia in recent years. Read brings together modern tools of formal logic and Bradwardine’s theory of signification to show that medieval distinctions can give great insight into the behaviour of semantic concepts such as truth. In a number of papers, I have developed a model theory for Bradwardine’s account of truth. This model theory has distinctive features:... Consequently.org -


Accommodation, Inference, Generics and Pejoratives Abstract: In this talk, I aim to give an account of norms governing our uses of generic judgements (like “kangaroos have long tails”, “birds lay eggs”, or “logic talks are boring”), norms governing inference, and the relationship between generics and inference. This connection goes some way to explain why generics exhibit some very strange behaviour: Why is it, for example, that “birds lay eggs” seems true, while “birds are female” seems false, despite the fact... Consequently.org -


Accommodation, Inference, Generics and Pejoratives Abstract: In this talk, I aim to give an account of norms governing our uses of generic judgements (like “kangaroos have long tails”, “birds lay eggs”, or “logic talks are boring”), norms governing inference, and the relationship between generics and inference. This connection goes some way to explain why generics exhibit some very strange behaviour: Why is it, for example, that “birds lay eggs” seems true, while “birds are female” seems false, despite the fact... Consequently.org -


Accommodation, Inference, Generics and Pejoratives Abstract: In this talk, I aim to give an account of norms governing our uses of generic judgements (like “kangaroos have long tails”, “birds lay eggs”, or “logic talks are boring”), norms governing inference, and the relationship between generics and inference. This connection goes some way to explain why generics exhibit some very strange behaviour: Why is it, for example, that “birds lay eggs” seems true, while “birds are female” seems false, despite the fact... Consequently.org -


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Generality and Existence I: Quantification and Free Logic In this paper, I motivate a cut free sequent calculus for classical logic with first order quantification, allowing for singular terms free of existential import. Along the way, I motivate a criterion for rules designed to answer Prior’s question about what distinguishes rules for logical concepts, like ‘conjunction’ from apparently similar rules for putative concepts like ‘tonk’, and I show that the rules for the quantifiers—and the existence predicate—satisfy that condition. Consequently.org -


Conditionals in Closed Set Logic Over the last couple of days on Twitter, I was involved in a thread, kicked off by Dan Piponi, discussing closed set logic—the natural dual of intuitionistic logic in which the law of the excluded middle holds but the law of non-contradiction fails, and which has models in the closed sets of any topological space, as opposed to the open sets, which model intuitionistic logic. \(\def\ydash{\succ}\)This logic also has a nice sequent calculus in which... Consequently.org -


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Accommodation, Inference, Generics and Pejoratives Abstract: In this talk, I aim to give an account of norms governing our uses of generic judgements (like “kangaroos have long tails”, “birds lay eggs”, or “logic talks are boring”), norms governing inference, and the relationship between generics and inference. This connection goes some way to explain why generics exhibit some very strange behaviour: Why is it, for example, that “birds lay eggs” seems true, while “birds are female” seems false, despite the fact... Consequently.org -


Accommodation, Inference, Generics and Pejoratives Abstract: In this talk, I aim to give an account of norms governing our uses of generic judgements (like “kangaroos have long tails”, “birds lay eggs”, or “logic talks are boring”), norms governing inference, and the relationship between generics and inference. This connection goes some way to explain why generics exhibit some very strange behaviour: Why is it, for example, that “birds lay eggs” seems true, while “birds are female” seems false, despite the fact... Consequently.org -


Defining Rules, Proofs and Counterexamples Abstract: In this talk, I will present an account of defining rules, with the aim of explaining these rules they play a central role in analytic proofs. Along the way, I’ll explain how Kreisel’s squeezing argument helps us understand the connection between an informal notion of validity and the notions formalised in our accounts of proofs and models, and the relationship between proof-theoretic and model- theoretic analyses of logical consequence. This is a talk for... Consequently.org -


What Proofs are For Abstract: In this short talk, I present a new account of the nature of proof, with the aim of explaining how proof could actually play the role in reasoning that it does, and answering some long-standing puzzles about the nature of proof. Along the way, I’ll explain how Kreisel’s Squeezing argument helps us understand the connection between an informal notion of of validity and the notions formalised in our accounts of proofs and models, and... Consequently.org -


Truth Tellers in Bradwardine's Theory of Truth Stephen Read’s work on Bradwardine’s theory of truth is some of the most exciting work on truth and insolubilia in recent years. Read brings together modern tools of formal logic and Bradwardine’s theory of signification to show that medieval distinctions can give great insight into the behaviour of semantic concepts such as truth. In a number of papers, I have developed a model theory for Bradwardine’s account of truth. This model theory has distinctive features:... Consequently.org -