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Questions tagged [logic]

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

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Do we need reason for “Not Doing” something? [duplicate]

Possible Duplicate: Does a negative claimant have a burden of proof? I have always wondered if NOT doing something requires reason like doing something does. As an example, do you think the ...
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2answers
300 views

How to distinguish premise in an argument

I am studying a logic text book and there is the following example which I don't get: Because I had decided, right off, that I liked John, what I heard in his answer was toughness and ...
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3answers
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Is the notion in Hume that you cannot deduce an “ought” from “is” related to his assertion that reason must be the servant of the passions?

I hear it asserted that David Hume said one cannot deduce an "ought" from an "is". I also find it asserted that he said reason must be only the servant of the passions. I had long uncritically ...
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Is it reasonable to arrive at a conclusion based on lack of evidence to the contrary?

I was having a discussion last night about my atheism, and it was suggested to me that agnostism is the only reasonable conclusion, as it leaves the door open for new information. This made me think, ...
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1answer
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Underlying logical structure behind Descartes' Ontological argument?

Quoting SEP: Version A: Whatever I clearly and distinctly perceive to be contained in the idea of something is true of that thing. I clearly and distinctly perceive that necessary ...
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What does Epistemic Closure mean?

I keep coming across this term and would appreciate it if someone could define it for me and also provide a relevant example.
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What is the difference between Law of Excluded Middle and Law of Non Contradiction?

In spite of reading the SEP entry under Contradiction several times I have difficulty distinguishing between the two. We can translate the Aristotelian language, with some loss of faithfulness, ...
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Is formal logic unsuitable for philosophical reasoning?

I'm taking a course at university about philosophical reasoning / argumentation. The professor came up with an example where formal logic was wrong: If Dave is in London, then he is in England. (...
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2answers
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There must be a reason we were given reason, no? [closed]

Let's assume that God created man for no reason, that there was no purpose (or goal or plan) to our general being. If there was no overall purpose to our being, then the only thing we can say about ...
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Falsifiability, facts, opinions, and tautologies

Wikipedia says: In the same way, "all men are mortal" is unfalsifiable: even if someone is observed who has not died so far, he could still die in the next instant. By contrast, "all men are ...
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Entailment/Presupposition in if-clause [closed]

In our semantics class we were arguing about the exercise 3.(7) from page 33 in Chierchia et al.: What relationship holds between the sentences in the following example?: a) "If John discovers that ...
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1answer
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Logical NOT of an Implication [closed]

How could you write NCpq in terms of moving the negation inside the conditional and keeping the conditional? The question got posed here originally by someone else. I can't post there at the moment, ...
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5answers
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Why is this set {CqCpq, CCpCqrCCpqCpr, CCNpNqCqp} the most common set of axioms for propositional calculus?

If you look, you can find many "equivalent", sufficient axiom sets for classical propositional calculus. The set {CqCpq, CCpCqrCCpqCpr, CCNpNqCqp} seems like the axiom set most commonly used. There ...
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3answers
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A special name for a proposition where the predicate is the subject?

Consider the following propositions: "I am me" "I am my Father's son" In both these cases, the predicate is the same as the subject by definition of the very subject and predicate. Is there a ...
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15answers
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Is there any rigorous philosophical basis for atheism?

Definition/Update In what follows I use the term God to refer to an entity that has at least one of the following properties: Has created the universe Is omnipotent Is omniscient Approaches to ...
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4answers
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How can we have a 'natural existence' for complex numbers? [closed]

For those who don't know what a complex number is, in simple terms, a complex number is the square root of a negative number! For example, the square root of -1 is called a complex number. Those ...
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10answers
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Are different values of nothing equivalent?

Are different values of nothing equivalent? Is 'no tigers' the same as 'no zebras'?
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What are the major research programmes in contemporary logic?

As an interested outsider who is prone to reading about different formulations of logic, I've become interested in better understanding the big picture of what people are trying to accomplish as they ...
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1answer
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What is the sense of the phrase “(no) fact of the matter about/as to”?

Could someone explain to me what exactly is meant by the phrase "fact of the matter about" (or "no fact of the matter about")? Another variant is: "(no) fact of the matter as to". In some cases, ...
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12answers
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Motivations for dialetheism?

At the request of the moderators, I've reformulated this question to change the emphasis of the question to something perhaps a little more broad-ranging: Question. What are the major modern ...
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4answers
444 views

Is there a logic that takes time into account?

I hope this is neither too simple nor off-topic; I apologize if so. I have just noticed that standard sentence logic seems to make assumptions about time in determining the truth/falsity of a ...
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2answers
105 views

Does it make sense to think that algorithms can be specified only for all that which is manmade? [closed]

I've been asking myself the following question over and over again: can one write an algorithm (a series of steps for solving a problem) for something that came about through a process that is at ...
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5answers
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Is it possible to generate logically valid sentences made up of “atomic contradictions”?

Is it possible to generate sentences that are made up of "atomic contradictions", but which remain logically valid as a whole? By "atomic contradictions", I mean atomic propositions that are not ...
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2answers
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Hempel's ravens (the confirmation paradox) [closed]

While taking a group of benefactors on a tour through the new aviary they had just helped to build, a noted ornithologist commented, "And here we have two of the finest examples of ravens that I have ...
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3answers
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What is a mathematical representation of the physical world?

Possible Duplicate: Was mathematics invented or discovered? To be more precise, does mathematics describe the physical world or does it describe a mental representation of the physical world? If ...
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What is fallacious about an argument that “I know X well, so she is right”?

I often hear from media personalities that they are right about a theory or assertion merely by associating themselves with someone or something. For example: "I know Mr. X very well (for years) and ...
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3answers
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Is it possible to deny that affirming a logical contradiction implies every possible proposition?

I find myself aligned with the motivation behind paraconsistent logic, they seem to me reason enough to warrant an attempt to structure logical systems which deny logical explosion. It does seem very ...
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5answers
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Why would definition not be proposition?

I've read in one mathematics book that any definition is not a proposition. Why is it so? What definition of proposition makes the former into the latter? EDIT: There is well-known analytic-syntactic ...
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2answers
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Does the law of excluded middle follow the law of excluded middle?

Example is that the word unknown is not unknown so it doesn't define itself. Similarly French is not French, it's in English, and "long" is not long and only 4 letters short. That's by example my ...
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3answers
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Is always lying about everything a consistency?

Here is another question I didn't get a clear answer to when the term "consistency" is applied in philosophy, logic and computer science. Is always lying consistent since we know the statements are ...
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3answers
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Is illogical = not logical?

I think law of excluded middle makes sense to mean that a statement should be either logical or illogical but in this case I don't assume "not logical" = "illogical" since the author didn't say "...
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1answer
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Should Wittgenstein be given some credit for Godel's incompleteness theorem?

Is there a connection between Wittgenstein's argument against the "Theory of Types" and the proof of Godel's Incompleteness Theorem? Being only semi-knowledgeable, I will draw the connection of which ...
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5answers
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Can a lack of knowledge or understanding invalidate a positive claim?

Consider the example of causal determinism. It can be phrased in many ways, all with identical meaning: - The idea that "every event, including human cognition and behavior, decision and action, is ...
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What are the necessary conditions for an action to be regarded as a free choice?

A common philosophical question revolves around the existence of free will, but what I've found is that these debates seem to gloss over the concept of "free will" itself, either taking it as a given ...
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Language as barrier to concepts [closed]

Can the limitations of language be considered a barrier in conveying a philosophical concept? How can an idea that resists linguistic formulation be conveyed without losing the essence? Is there a ...
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10answers
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Is the universe isomorphic to a universal turing machine?

I often think about problems that require an understanding of the very essence of computation and its inherent limitations. So, my questions are as followed: Is the universe isomorphic to a universal ...
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Is the argument that a claim is “too strange to be made up” an appeal to logos or pathos?

When someone tries to persuade you of the truth of something they said and they use the argument that it is too strange to be made up (or any variations of this, such as "too complicated to be fiction"...
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What does Hegel mean by “Quality”?

In the Science of Logic, Hegel initially presents quality as existent determinateness. He further distinguishes two modes of determining quality in accordance with the moments of existence: ...
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Is reductionism the primary means of logical analysis in analytic philosophy?

I was reading a philosophical article about analytic philosophy and I saw the claim: Russell and many philosophers influenced by him asserted that complex statements can be reduced to simple ...
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4answers
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Where is the weakness in the ontological proof for God's existence?

I read the ontological proof for God's existence. As much as I understood, it says that if you consider that existence is part of essence, then the most complete essence should also exist. Now, I see ...
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What does it mean that a claim is a claim of nonexistence?

This question has devolved into a discussion. As I understand the discussion, everything is revolving around the veracity of statement Nonexistence can never be proven. and on what exactly ...
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13answers
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Does a negative claimant have a burden of proof?

I have often heard it said that the burden of proof is on the positive claimant but not on the one making a negative claim. A person claiming, "God exists" has a burden of proof but not a person ...
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3answers
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Are systems of logic that don't follow or extend garden-variety FOL possible?

As I know all humans share a unique logic and even less-educated people uses same common sense in their statements. For example, it is rational for anybody that if P is correct then P or Q is correct ...
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What is the difference between “reductio ad absurdum” and “proof by contradiction”?

What is the exact difference between reductio ad absurdum and proof by contradiction? Wikipedia used to state that: Reductio ad absurdum (Latin: "reduction to the absurd") is a form of argument in ...
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Does philosophy belong to empirical science or formal science?

According to Wikipedia, science can be divided into empirical science (such as natural science and social science) and formal science (such as mathematics, logic, statistics). I was wondering if ...
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2answers
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An immovable object and an irresistible force [closed]

If an immovable object is an object that cannot be moved no matter what and an irresistible force can move anything, what would happen if an irresistible force is used on the immovable object?
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1answer
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When it is correct to use Tarski's undefinability theorem versus Gödel's incompleteness theorem?

Smullyan (1991, 2001) has argued forcefully that Tarski's undefinability theorem deserves much of the attention garnered by Gödel's incompleteness theorems. That the latter theorems have much to say ...
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4answers
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Are there any potential flaws in the definition of validity as “provable or falsifiable”?

I have made an argument in another thread that a proposition must be provable or falsifiable to be valid. Are there any flaws in this definition of validity? What might be a potential counter-argument ...
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What is the philosophical equivalent of mathematical proofs?

In mathematics, there seem to be five standard methods of proving or refuting an argument: a proof by induction, contradiction, counter example etc. Are there some typical proof methods that exist in ...
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Is the claim “this coin is fair” falsifiable?

Wikipedia says, The claim "No human lives forever" is not falsifiable since one would have to observe a human living forever to falsify that claim. Thinking on similar lines, even if the ...