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Use this tag for general questions about logic that are not categorizable under some more specific tag, like "mathematical logic", "informal logic", "classical logic", etc.

2 votes
2 answers
155 views

Arguments Against Plural Quantification

What are some good arguments against taking plural logic, a slight extension of first order logic with plural quantification as a foundational logic? … The SEP article also mentions some results like the equi-interpretability of monadic second order logic and plural logic as justification for the ontological innocence of plural logic. …
Greg Nisbet's user avatar
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2 votes
1 answer
155 views

Rejecting the principle that any proposition can be meaningfully negated

Your argument in (1) that all logics have to be closed under negation seems to rest on the assumption that a logic should consist of all meaningful expressions in some context. …
Greg Nisbet's user avatar
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0 votes
1 answer
526 views

Describing differences between "computational" and "non-computational" proofs

Let's call the resulting proof in our refinement logic-inspired system H. …
Greg Nisbet's user avatar
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2 votes
1 answer
190 views

Are there modern approaches to logic that aren't *grounded* in math?

In fact, you may think what we are doing isn’t really "logic" at all, but more philosophy of language, or even philosophy of mind or epistemology. Why then call it logic? … It suggests but does not directly claim that conflating an application of logic and logic itself obscures some important and interesting ideas. …
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1 vote
0 answers
30 views

disjointness in logics with higher order plurals

Have disjoint and non-disjoint flavors of higher-order logic with plural quantifiers both been studied? …
Greg Nisbet's user avatar
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0 votes

Approximately directed graph of logic types

The single, most important logic is classical first-order logic (henceforth FOL). … , dependence logic. …
Greg Nisbet's user avatar
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35 votes
Accepted

How is the argument "I love all logic, but I don’t love deductive reasoning. Therefore, the ...

What kind of manipulation is valid formally changes from system to system (e.g. in intuitionistic logic vs classical logic). … Classical logic, however, doesn't give us the ability to talk about causality. …
Greg Nisbet's user avatar
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4 votes
1 answer
234 views

How do you work with a non-classical metatheory?

I'm interested in nonclassical logic, particularly propositional logics because you only have one type of non-logical symbol. … The most powerful for propositional logics, in my opinion, is just translating formulas inductively into a classical first order logic with a single sort. …
Greg Nisbet's user avatar
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2 votes
0 answers
210 views

What are the consequences of rejecting identity of indiscernibles

(c≠d)∧(P(c)↔P(d)) Are there any go-to paradoxes / counterintuitive results if we take (3) as an axiom in a second-order logic system? …
Greg Nisbet's user avatar
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1 vote
1 answer
296 views

Are there useful logics that reject disjunction introduction?

Here's a somewhat artificial example of a three-valued logic constructed not to admit disjunction introduction while still having fairly symmetrical truth tables and agreeing with classical logic when … Here's a three-valued logic that doesn't admit disjunction introduction, and has the connectives K (conjunction/koniunkcja), A (disjunction/alternatywa), and C (implication/implikacja). …
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0 votes
1 answer
73 views

Non-equivalence of `i`-form and a claim of existence

In traditional logic, the following inference is valid All As are Bs. AaB ----------------- ----- Some As are Bs. …
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0 votes

Why is any sentence a logical consequence of a set of inconsistent premises?

I'll discuss classical propositional logic. Let M (for "model") be an intepretation. We can make M just a set of variables that are true, e.g. {A, B, C} or similar. … This is a specialized topic within logic, but people do study systems of logic that are specifically designed to avoid certain paradoxes or counterintuitive behavior like consequences following from contradictory …
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2 votes

Prove that if S tautological consequence of P, S tautological consequence of Q, then S tauto...

So, the conditional theorem below is correct. P ⊢ S Q ⊢ S --------- P∨Q ⊢ S The conditional theorem is only false if there's a case where the premises are true and conclusion is false. And simi …
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0 votes

Variant of free logic that accepts domain emptiness but rejects non-referring terms

The variant of free logic that permits domains to be empty, but rejects non-referring terms is simply first-order logic. … Some presentations of first-order logic allow the domain to be empty, others require it to be non-empty. …
Greg Nisbet's user avatar
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0 votes

Help needed with predicate interpretations- Wilfrid Hodges logic

So, we want to encode the following sentence fragment in first-order logic: nor may any true gentlemen be punished with shipping, unless his crime be very shameful, and his course of life vicious and …
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