Questions tagged [logic]

For questions about logic, whether it concerns syllogistic logic, mathematical logic or the nature of logic itself.

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Does a formal fallacy definition for “X has not happened (with potential time constraint Y), so Z will not happen (now or in near future)” exist?

Does there exist a formal definition for (what I would say is) a logically fallacy that would fit to the following structure of statements: "X has not happened (with potential time constraint Y), so ...
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Before Gödel, was undecidability of axiomatic systems an issue at all?

Before Gödel, was the issue raised that there may be undecidable statements within axiomatic systems of thought? Gödel managed to answer affirmatively by proving that the assumption of the ...
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In Quine's ontology, why does a 'recognition' of something lead to ontological commitment while a 'feeling' does not?

We are discussing Quine's On What There Is in a metaphysics class I am in. I felt like I understood what he meant, that if something has to be predicated for in a sentence, we are ontologically ...
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Is there a logical argument for the limit of knowledge?

It is justifiable to assert that certain knowledge could not be disseminated without the invention of writing. One could say that humanity needed the knowledge of writing before further knowledge ...
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111 views

How do proofs about logic fit into a logical framework?

I'm learning logic from Michael O'Leary's A First Course in Mathematical Logic and Set Theory. In chapter 1 he carefully explains the meaning of logical implication (p ⊨ q), logical inference (p ⟹ q), ...
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Proving A ⊨ B iff ⊨A → B

Let A and B represent arbitrary formulas. Also let 1 ≡ True and 0 ≡ False Prove that A ⊨ B iff ⊨A → B For my proof, I break down the biconditional into two conditionals and prove each conditional. ...
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52 views

About Wigner's view on the relation between mathematics and physics?

Physicist Eugene Wigner argued that the enormous usefulness of mathematics in the natural sciences is something bordering on the mysterious and that there is no rational explanation for it ...
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1answer
106 views

Did Stephen Hawking think that logic is contingent on physics?

According to this book*: Extrasensory Perception: Support, Skepticism, and Science, it says that Stephen Hawking thought that logic was contingent on physics, i.e that logic depends on the physics of ...
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Name for this Logical Fallacy

Suppose there is a non-empty subset A of U. Let A' denote the complement of A in U. What is the name of this logical fallacy? X is true for A therefore not X is true for­­­­­­­­­­­­­­­­­­ A' ...
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42 views

Does anyone have an example where a sufficient condition comes first?

Example: Sufficient Condition of A+ MUST MEAN Necessary Condition of Studying occured Temporally speaking, either condition can occur first, or the two conditions can occur at the same time. In our ...
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logical atomism explanation with examples

I read a bit of logical atomism by Russel but would appreciate if someone explains with examples of what is meant by it. For example it says:" According to logical atomism, all truths are ultimately ...
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Is there a term for such a logical fallacy?

I'm wondering if there is a terminology for the following logical fallacy: Joe: Statement "X" must be true because it is clearly laid out as such in mutually reliable source "Y". Sam: Joe, the ...
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Term for evidence that isn't understood

Imagine someone asks how you can believe that whales evolved from land animals. You tell them about "missing link" fossils that chronicle whales' evolutionary journey. This is solid evidence - to ...
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Learning Logic, A Pathway

I would like to devote a greater amount of time to further learning logic. I have experience with mathematical proofs and thus have an understanding of logic to the degree necessary for proofs. I ...
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76 views

Is there a logical fallacy to identity politics?

My understanding of Identity Politics goes as follows: A is a member of/identifies with group X B is not a member of/does not identify with group X A frames challenge S in terms of X Because B doesn’...
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Where did Suárez say the principle of non-contradiction does not apply to the Trinity?

Fr. Réginald Garrigou-Lagrange, O.P., says, in Le Sens du Mystère et le Clair-Obscur Intellectuel: Nature et Surnaturel p. 128 fn. 1 (Engl. transl. p. 142 fn. 41): St. Thomas never would have ...
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What is the meaning of Principle C'' in Hartry Field's 'Science Without Numbers'?

For Field, the following is 'perfectly obvious', but I would like confirmation that I understand it completely. Let A be a nominalistically statable assertion. Let A* be the assertion that results by ...
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170 views

Why do people use the material implicaton over alternatives?

It isn't because it works. There are numerous alternative, fully-functioning implication systems. If people have a problem with conditionals with false antecedents, and with true consequents, always ...
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Is there a semantically complete system of direct-method deductive logic?

Does anybody know of a system of direct-method deductive (propositional) logic, in other words, a system that does not require (or even incorporate) conditional (and indirect) proof method(s) and that ...
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What is an enumerative definition?

W. Kent Wilson in his book argues for developing an enumerative definition of concepts. An enumerative definition formulates its meaning by enumerating the objects or phenomena that fall under the ...
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35 views

Why is the material conditional a thing? [duplicate]

If people have a problem with conditionals with false antecedents and with true consequents always being true, why not just change it according to what is found to be more intuitive? Regarding ...
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What reasons do I have to believe that ~p->~q and pV~q are equivalent?

I understand the reasoning for why pVq implies ~p->q, but not the converse. What reasons are there to believe ~p->~q implies pV~q, other than to make the whole material implication system neat?
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Does denying the Limit Assumption in counterfactual logic lead to contradiction?

According to the similarity semantics for counterfactuals, a counterfactual A > C is true iff on the most similar class of worlds to the actual world (or any given world the counterfactual's truth ...
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Can/Do there exist any quantifiers other than “there exists” and “for all”?

I'm curious about why there are only the two logical quantifiers there exists and for all. Intuition and human language support the idea that these quantifiers make sense, but otherwise it seems ...
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What did Gödel mean by “positive property” in his ontological argument?

In his ontological proof, Gödel states (Axiom 1) If a property is positive, then its negation is not positive. What does he meant by this term? I have come across authors who replace this notion ...
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281 views

Is God's existence either impossible or necessary?

This is meant as a supplement to a modal ontological argument to show that God's existence is either logically impossible or necessary. Am I committing a fallacy or a logical error of some kind or ...
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138 views

Wittgenstein and “linguistic trap”

In a book on philosophy I've lost by now I encounter an argument about "linguistic trap" idea attributed to Wittgenstein, that is, such a trap is supposed to be "taking linguistic convention or ...
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113 views

Bibliography about non-mathematical applications of logic:

I have been recently playing with modal and temporal modal logics in the context of "organisms" (mostly after some study of entelechy in Aristotle and relatedly, some ideas of current biology). I have ...
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When thinning on the right how is it correct that the number of formulae on the right can be increased from zero to one?

I understood there being no formulae to the right of the turnstile as meaning that the formulae on the left was inconsistent. However, my textbook writes that there is a special case of thinning on ...
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Is this statement self-defeating?

Would the statement "I don't want to talk about cars" be a self-refuting statement in that the statement itself "talks" about cars?
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How to show (in a hand waving manner) that the Godel sentence is true

I have been reading Graham Priest's The Logic of Paradox, and there is a section where he tried to show that our informal proof argument (in Priest's terminology, naive proof procedure) is more ...
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Can these selfreferential statements be rewritten as such?

This statement is a paradox = this statement is both true and false this statement is a hypodox = this statement is either true or false this statement is a contradiction/always false = this ...
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156 views

always false vs necessarily false , is it the same?

according to the basic tenets of classical propositional logic, contradictions are 'always false' tautologies 'always true'. When it is extended to modal logic we have the notions of 'necessarily ...
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Kant claimed that 7+5=12 is a synthetic proposition; is this not obvious?

Whenever anyone claims that 7+5=12 is an analytic proposition, they are overlooking one important detail. What is that? Charles M. Saunders
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If cause C has the mutually exclusive effects Y and Z, then is causality held? Why?

Imagine there is a cause but several effects. Of course determinism is not held, but my question is about causality. If cause C has two mutually exclusive effects Y and Z, then at each given time ...
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Logical Notation in Anscombe's “Causality and Extensionality”

In "Causality and Extensionality," Anscombe writes thus: Our argument uses the description of a class—say x̂(Gx · p), assuming G to be a respectable class-forming predicate. Let G be such that x̂(Gx) ...
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Heraclitean, Parmenides, and Aristotelian change? Is there an alternative?

Dear philosophy stack exchange, I've been considering of late the problem of change as presented by Heraclities and Parmenides as well as the supposed solution to the problem by Aristotle himself. I ...
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Question about conditionalization and probability

I am working on a problem set and I am not sure if I am heading in the right direction. The scenario: "Suppose three identical boxes are presented to you, and you are told that one box contains two ...
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Question about anchoring and adjustment (Tversky and Kahneman) and why anchoring often yields correct judgments

I am working on a problem set and I am having some difficulty wrapping my head around a concept introduced by Tversky and Kahneman. My problem set asks the question "Why does anchoring nevertheless ...
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583 views

If other versions of us existed in a multiverse, would we be morally responsible for the actions of these alternate versions of us? [closed]

Hypothetically, if we lived in a multiverse which contained an infinite number of identical versions of each of us containing our respective memories and experiences, with the exception of key ...
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This statement is in a disjunction with itself

Are the following listed statements equivalent? 1: (1) is in a disjunction with (1) 1: (1) is in a disjunction with (1) OR 1: (1) is in a disjunction with (1) (the intended meaning of (1) is '...
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Can supervaluationism relate to the abortion debate? If so, how?

So I'm writing an essay on the Sorites paradox and how it relates to the abortion debate. One resolution to the paradox I was reading about came from supervaluationism, but I'm not entirely sure if or ...
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How can one prove ∃𝑥(𝐹(𝑥)→𝐺(𝑥)) given the premise ∃𝑥𝐹(𝑥)→∃𝑥𝐺(𝑥)? [closed]

Premise: ∃𝑥𝐹(𝑥)→∃𝑥𝐺(𝑥) Desired Conclusion: ∃𝑥(𝐹(𝑥)→𝐺(𝑥))
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Is it possible for an argument to be logically valid but not truth-functionally valid?

Truth-functionally valid: there is no truth value assignment for which the premises (of an argument) are true yet the conclusion is false. I am told that there are arguments which are logically valid ...
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102 views

Are Pathos, Logos, and Ethos equally valid?

The three main ways of reasoning are Pathos, Ethos, and Logos. I have tended to see Pathos as inferior to Ethos and Logos because it appears to rely more on emotions than on facts. But does it really ?...
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Which of common rules of inference are rejected on some philosophical grounds?

My question is: is there a mathematical or philosophical basis for rejecting any of the following rules of inference? If yes, then what is the argument for rejecting any of them? I am asking this ...
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Question about v-variants of variable assignments

In Full Predicate Calculus, some variable assignment q satisfies a disjunction under interpretation U if q satisfies one or both disjuncts under U, it satisfies a conjunction under interpretation U if ...
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1answer
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Is it true that an argument cannot be both inductive and cogent?

I have been asked a question in class where we would need to pick out the false statement from a given set of options. The problem is that I am not really sure why my answer was wrong? Here is the ...
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Is Kant's transcendental logic a kind of erotetic logic?

In the first Critique, Kant presents a "problematical" concept of the ideation of reason, e.g. he talks about a focus imaginarium or something at one point. And his discourse on noumena as not "...
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How can the mere observation of race (without an assertion of equivalence) logically be considered racism?

During a social situation in which one observes the race of a person, I have heard the argument that it is racist to refer to that person by his or her race. Let's say that I have "hypothetically" ...