Questions tagged [logic]

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.

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Arguing / Pretending as an Opponent Speaker

What do you call a person or the strategy where the speaker acts as the opponent to know the issue at hand better (as an opponent). For instance, a Vegan (person X) can argue with another Vegan, ...
Tanvir's user avatar
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Natural Deduction flagging system (Virginia Klenk)

I am wondering if anyone can clarify a detail that's been bugging me. Here are the flagging restrictions for Virginia Klenk's natural deduction system: RI. A letter being flagged must be new to the ...
Casey's user avatar
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Is the following derivation of predicate logic correct?

I recently discovered https://proofs.openlogicproject.org/, except I'm still figuring out the appropriate rules that are needed for the system to check my proof. I thought it'd be quicker to turn to ...
part-two's user avatar
3 votes
8 answers
547 views

Is ancient indian philosophy outdated?

I know in the West one would be taught Western philosophy but even here in India generally, the colleges and unis don't teach ancient Indian philosophy (yes there are exceptions like IITs but very few)...
Rey Gomez's user avatar
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2 answers
206 views

How could Britannica's explanation of Venn diagrams work?

Britannica.com/biography/John-Venn says the rings on the left are a Venn diagram of the syllogism “Some mammals are carnivores; all mammals are animals; therefore, some animals are carnivores” but ...
Robbie Goodwin's user avatar
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1 answer
147 views

How to make this argument valid?

If Peter is virtuous, he manages a household with patience. If Peter is to be good, he needs patience. Here's my attempt to understand 1 and 2. I get confused by the wording and necessity-sufficiency ...
part-two's user avatar
1 vote
1 answer
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Checking translations of predicate logic

Let Dx = "x is a detective", U12 = "1 is the uncle of 2", and appropriate lowercase letters for names. If there are any detectives, John is the only detective. No detective is ...
part-two's user avatar
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so im arranging these arguments from strongest to weakest, and am confused?

Either reublocrats are uninformed, or democrans or independents are uninformed it is not true that republocrats are uninformed someone is uninformed either republocrats are informed or they are not ...
Janeiro Ahlan's user avatar
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3 answers
210 views

Checking the validity of an argument

Is the following argument valid? If A is to be good, they must be just If B is to be good, they must be just Therefore, if C is to be good, they must be just Therefore, if C is just, they become good ...
part-two's user avatar
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1 answer
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If this world is the only possible world, what does that mean for validity in logical arguments?

Validity is usually defined in terms of possible worlds. More specifically, an argument with premise set S and conclusion C is said to be valid if and only if there is no possible world with all the ...
user107952's user avatar
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Issue with the interpretation of Propositional Logic

I’m having an issue with the terminology and perception authors use. Some authors perceive PL as a branch of logic “with subsets” with classical or truth-functional PL as these subsets. Other perceive ...
Jack Frosher's user avatar
1 vote
2 answers
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What are some strong arguments for logical holism?

What are some strong arguments for logical holism? The idea that the world operates in such a way that no part can be known without the whole being known first seems extremely foreign to me. This is ...
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How to prove that ((~A->~(A->B)))->A is a theorem in Sentential Derivation

I've been banging my head against this question (HW) for the last few hours, and I'm not able to answer it. This is based upon the Logic Book 6th Edition I've been using negation elimination, in order ...
Unknown Unknown2's user avatar
-1 votes
1 answer
169 views

Can someone explain why this immediate inference is valid?

everyone. Thank you very much in advance for any help you can give me with this issue. I'm enrolled in an Introduction to Logic course, and we're currently working on Categorical Propositions. I've ...
sixo33's user avatar
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1 answer
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Lewis's truth condition for counterfactuals

According to SEP, Lewis's theory of counterfactual conditionals defines truth for counterfactuals as follows: [...] the truth condition for the counterfactual “If A were (or had been) the case, C ...
Rainer_Zoufal's user avatar
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2 answers
227 views

A question about the Addition rule

Propositional logic Natural Deduction The Rules of Implication of Addition says: p Therefore: p or q This rule doesn't make sense, and my book doesn't explain it. Rather, it just expects me to accept ...
Dasem's user avatar
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4 answers
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A logical approach to the question of God

I am trying create a logical approach to the question of whether there's a creator or not, but I have a few questions. Before that though, I'll outline what I have currently: Something started ...
A. Kvåle's user avatar
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Why do equivalent propositions sometimes differ in apparency?

I study maths, and I have found that a useful way of thinking about two propositions A and B being equivalent is to regard them as being two different ways of saying the same thing, or equivalently, ...
legionwhale's user avatar
1 vote
3 answers
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Would quantum uncertainty in neurons mean free will or just random will?

Famed physicist Penrose has an interesting albeit speculative theory that tiny structures in the Neuron facilitate conciousness beyond the way we currently think neurons work. Whether he's right or ...
john doe's user avatar
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2 answers
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I read lots of introduction books about philosophy, now I want to learn more. Reccomend some books thar are not too basic or too advanced

What should I read? Should I read the books philosophers themselves wrote or the ones that is written by someone else??? I don't want books that only give introduction. I read lots of easy ...
Monica AMen's user avatar
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1 answer
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Formal proof in choosing between two competing assertions regarding fraudulent/honest claims?

Please provide formal proof (or near enough, according to ability) for your decision as to which of the following two assertions is correct: "Even if a claim is arrived at fraudulently, that ...
Theo d'Or's user avatar
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2 answers
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Question on Godel's Remark on Algorithmic Nature of Mind

Gödel claimed that what the Theorems do entail (specifically, the Second Theorem) is that mathematics is inexhaustible: It is this theorem [i.e., the Second Theorem] which makes the incompletability ...
Ajax's user avatar
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In the modern square of opposition are contradictory relations logically equivalent or not?

Initially, I suspected no because categorical propositions that have contradictory relations according to the modern square of opposition will always have opposing truth values. For instance, if we ...
Slecker's user avatar
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2 answers
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Some doubts on Incompleteness Theorems

An important point to note about first incompleteness theorem is that while a certain formula is "true" but unprovable, it is "true" on the basis of my understanding (intended ...
Ajax's user avatar
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4 answers
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Is "sometimes necessary" valid in necessity and sufficiency

I recently learned about this concept and in discussing with a peer, I was wondering, is it ever right to say "x is sometimes necessary but not sufficient for y to be the case". In my mind I ...
ParthianShotgun's user avatar
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1 answer
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Mistake in Kenny's New History of Western Philosophy

I have been reading the chapter on logic in Ancient philosophy and I think I have noticed a mistake. On page 96, Kenny introduces Aristotle's syllogism with: Every Greek is human, Every human is ...
user80873's user avatar
1 vote
1 answer
179 views

Is Tarski's theory of truth widely accepted

Tarski's truth theorem asserts that a truth definition for a (reasonably strong) theory cannot be formalized within that theory. It seems that Tarski's theory of truth has met with a lot of criticism. ...
Eugene Zhang's user avatar
3 votes
1 answer
80 views

What part of a universal propositions is the antecedent?

The wiki article on vacuous truth says: a vacuous truth is a conditional or universal statement that is only true because the antecedent cannot be satisfied. I'm familiar with identifying the ...
Slecker's user avatar
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1 answer
158 views

i don't understand modus ponens

I'm learning about modus ponens in propositional logic but it doesn't makes sense to me I can think of an examples where a true premises leads to a false conclusion: p -> q p Therefore q If the kid ...
Dasem's user avatar
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2 votes
1 answer
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Does the Aristotelian standpoint agree with the Boolean standpoint on existential import when talking about non-existent things?

According to the Boolean standpoint, it rejects the notion that a universal statement implies existence. For instance, the statement "all S are P" does not tell us whether or not any members ...
Slecker's user avatar
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2 answers
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What kind of fallacy is "X have this property, Y have this property too, so Y is X"?

Let's say someone states "One well-known property of tables is that they are supported by four legs. This chair is supported by four legs. So this chair is a table". What kind of fallacy ...
David's user avatar
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Does the quantifier 'all' satisfy the definition of the quantifier 'some?'

Since 'some' means at least one and 'all' refers to an entire group of things then at least one member of that group is being referenced thus satisfying the definition of 'some,' right? If this is the ...
Slecker's user avatar
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0 answers
70 views

What is the "logic of ejaculations"?

I was looking through a paper on one valued logic and it references something called the "logic of ejaculations", shocked by the name, I tried to find another reference to it in which I ...
Bradly O's user avatar
4 votes
4 answers
482 views

Is Logic necessary to prove its own existence?

These are propositions I take to be true: Our knowledge is based purely on empirical observation. There is no way to directly observe reality or objective truths. Therefore, there is no way to say ...
AnanthaKrishna K's user avatar
1 vote
1 answer
95 views

How to prove consistency of theory with metalanguage?

I am familiar with first-order model theory. I also know that Tarski's definition of truth was made precisely in order to avoid paradoxes related to metalanguage such as the Liar. My question is: how ...
Matteo Casarosa's user avatar
3 votes
2 answers
307 views

Philosophers or philosophical traditions that reject symbolic reasoning

I'm most familiar with philosophy in the context of discussing various flavors of logic, such as independence-friendly logic, various extensions of first-order logic with plurals, relevant logic, and ...
Greg Nisbet's user avatar
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1 answer
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What does it mean for one geometrical axiom to be considered _equivalent_ to another geometrical axiom?

What does it mean for one geometrical axiom to be considered equivalent to another geometrical axiom? For example consider Playfair`s axiom: In a plane, given a line and a point not on it, at most one ...
Euclid Looked On Beauty Bare's user avatar
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1 answer
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Is it useful to be able to define complex words with many definitions?

Greetings fellow earth dwellers. Definitions...useful, sharp, often-times dust clearing, so to speak. But as one progresses into intellectual conversations, definitions aren't so clear and can be ...
sometimes this sometimes that's user avatar
4 votes
6 answers
2k views

Does there exist truly objective thoughts?

Today I was arguing with my friend that the colour of sky is subjective. I claimed that the colour of sky is a subjective idea and a person who is colour-blind may perceive it as a different colour. ...
tryst with freedom's user avatar
1 vote
4 answers
108 views

Is identity unique and is it valid for only a given time?

Is identity unique and is it valid for only a given time? A river is not the same and changes constantly. Even the same can be said about a chair, so is identity bound to a time y and bound to a ...
Sayaman's user avatar
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1 vote
2 answers
154 views

Is demanding an ureasonable and unrealistic amount of sources a logical fallacy?

Let's suppose the following: Person 1: All scientists agree that the sun is real. Person 2: Oh yeah, why don't you list every single scientists as proof? Here's another example: Person 1: Humanoid ...
PotatoPotato's user avatar
1 vote
3 answers
321 views

In the context of philosophical logic, what does 'extra-logical' mean?

I am having trouble understanding what 'extra-logical' actually means in the context of philosophical logic. Case in point: Bueno and Colyvan argues in their paper Logical Non-Apriorism and the ‘Law’ ...
Constantly confused's user avatar
0 votes
2 answers
69 views

Do different elements of logic have different epistemological strength?

Do different elements of logic have different epistemological strength? By epistemological strength, I mean epistemological certainty or the certainty the concept is true and grounded on truth. For ...
Sayaman's user avatar
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0 votes
2 answers
291 views

Are the premises of deductive arg's. founded upon inductive cases?...help is what I am in need of

Let's take this example of a deductive argument: P1: Monkeys like bananas. P2: Lucy is a monkey. C: Therefore, Lucy likes bananas. Disregarding whether this argument is true or false, how does one ...
sometimes this sometimes that's user avatar
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2 answers
116 views

Is identity a construct or something real?

If race is a social construct, then is identity also a construct? Is identity the concept of something being itself something that exist in the world or something abstract that doesn't exist in our ...
Sayaman's user avatar
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1 vote
2 answers
246 views

What makes a fallacy... a fallacy?

According to Wikipedia, a fallacy is "the use of invalid or otherwise faulty reasoning, or 'wrong moves' in the construction of an argument". I'm curious, however, about how are some things ...
Jp_'s user avatar
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2 answers
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Paraepistemic logic?

Suppose a u-operator for "it is understood that" and a k-operator for "it is known that"; let S stand for various sentences. Here are some possible rules for relating these: uS → ...
Kristian Berry's user avatar
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1 answer
61 views

Does it make a difference to logic if the law of identity is never true instead of being sometimes true?

Does it make a difference to logic if the law of identity is never true instead of being sometimes true? It seems like when we don't consider the law of identity is not an axiomatic truth, we assume ...
Sayaman's user avatar
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-1 votes
6 answers
1k views

What things can't logic or doesn't our logic know, see or explain?

For beginning, it is arguable that for example logic knows the POSSIBILITY of the existence of matter and the result of a 'deterministic' 'causal' 'mechanical' system. PART 2: FEATURES OF LIFE OR SOUL ...
Koorosh's user avatar
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1 vote
4 answers
1k views

Why is non-binary logic not commonly used?

This question has been modified in response to a comment. While many-valued logic exists, rarely is it used. People primarily just use binary logic. Is there a reason for this? So many-valued logic ...
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