# 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 Cox's theorem implicitly assumes the three classic laws of thought?

I read about Cox's theorem a long time ago in "Jaynes Probability Theory: The Logic of Science". It was used to justify the so-called "logical" interpretation of probability. My impression was that ...
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### What is the problem with using circular reasoning? Is it "invalid"?

What, specifically, is the problem with circular logic/reasoning? I think it's invalid. For some reason, everyone knows that it's wrong to use, but is there anything more to it than that? ...
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### How did first-order logic come to be the dominant formal logic?

Early formal systems like Frege's Begriffsschrift or the Peano's work on the axiomatization of the natural numbers used axiom system with an underlying second-order predicate logic (from today's point ...
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### Are there any known deficits of "relevant logic"?

The principle of explosion is the law of classical logic and similar systems of logic, according to which any statement can be proven from a contradiction. Some early formal systems like Frege's ...
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### Is "nothing" easy to understand? [closed]

Let's first define nothing as the absence of something. Not talking about universe here. How early on do we grasp this concept of nothing? Are there people who get old without that basic ...
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### Is implying the same as asserting?

I need to understand if implying something, knowingly or unknowingly, is the same as asserting it. I also need to understand if it is merely semantics or there is a philosophical rigor to it. EDIT: ...
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### How does Robert Nozick explain the Gettier problem?

Nozick agrees that the Gettier counterexamples to the JTB analysis of knowledge are cases where someone has a JTB but does not know. What is his explanation of what has gone wrong in those cases? ...
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### Does Wittgenstein's Tractatus establish serious bounds for discussions of the supernatural from a modern point of view?

In today's mathematics, we have many variants of logic (propositional, first order, higher order, fuzzy logic, etc.). These are all self-consistent formal systems that are based on some set of axioms. ...
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### Is reductio ad absurdum a valid logical proof?

It strikes me that atheists often in the religion debate will try to characterize religion in a funny or silly way, often comparing religion to belief in fairies or unicorns or flying spaghetti ...
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### Is it possible in any way to justify murder using reason or logic?

Some believe that murder is only committed due to an emotional or moral action, but can you ever justify it with reason?
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### Possible worlds in logic

In modern logic there is often talked about possible worlds. I understand this idea in this way: Every proposition may be true or false. Possible world W is a set of all propositions where there is ...
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### How to be a good critic?

How can we be a good critic when facing people's rigid beliefs? I'm interested in how to attack (logically) their dogmatic beliefs to have a "good" influence on their minds, because if we just attack ...
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### an argument about a logic question

I've had an argument with someone and I would like to know for sure if I'm right. I don't know if you have heard of the board game "Catan", it's not really important. Well, long story short, at the ...
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### Can an eternal god destroy himself? [duplicate]

Possible Duplicate: Is the definition of God consistent? (primary) also: An immovable object and an irresistible force God's paradoxes and their implications To many, at first sight, ...
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### What are the philosophical implications of category theory?

I have heard about topoi being the ideal entities to use for foundations of mathematics (since we are able to reasonably interpret our theories in them), so I imagine there might possibly be some ...
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### When given limited information, is the simplest solution that matches that information most likely correct?

Is there any basis in philosophy for the idea that when given limited information, the simplest solution that matches that information should be presumed correct or most likely to be correct? For ...
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### Syllogism from Lewis Carroll

I was reading Code by Charles Petzold, and on page 86 he references a syllogism from Lewis Carroll: All philosophers are logical; An illogical man is always obstinate; Therefore, some obstinate ...
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### What is a mathematical or logical name for the process of proving a statement by exhausting the problem domain?

I am trying to understand logic and I came across a set of actions that I describe below that I can't get my head around. Suppose you have a bag of multiple colored balls. Situation 1. Argument: ...
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### What is Kant's argument about the relationship between logic and reason?

At Wikipedia, I read: Logic arose (see below) from a concern with correctness of argumentation. Modern logicians usually wish to ensure that logic studies just those arguments that arise from ...
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### A bizarre question asked at a job interview about conditional probability [closed]

I was recently asked a "logic puzzle" type question at a job interview which seems to be a slightly mangled version of a N-coin puzzle (intended to test the subject's knowledge of conditional ...
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### Term for a reduction to an unanticipated result

I'm looking for a term that describes the logical argument I am making. Both to just have a way to describe it and ensure that it is indeed a sound argument. Somewhat formally the argument is as ...
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### Seemingly invalid piece of reasoning in The Republic

In the beginning of The Republic, when discussing the nature of justice, Socrates leads Polemarchus to agree with him in this line of reasoning (the numbering is mine): But let us consider this ...
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### How to get started with philosophy without getting overwhelmed quickly?

I’ve spent a lot of time trying to find how to get started with philosophy but I can’t. It seems that getting started with computer programming is nothing in comparison - with computer programming it’...
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### Does the phrase "vacuous tautology" have specific meaning?

I just came across a use of the phrase "vacuous tautology" used in a piece of writing. Now, based on my understanding, by definition a tautology has no content and is therefore always vacuous. This ...
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### Is there a category or grouping of logical strategies that focuses on "anti-fallacious" techniques?

Original Question: I am a newbie, but am interested in some perspective here. I find it fascinating to examine and read about fallacies commonly used as techniques to gain an upper hand in debate. ...
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### Name for this illogical technique?

I recently noticed a pattern of interaction with someone. This person will start talking about something, give overly elaborate explanations that wander wildly between disconnected ideas, often using ...
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### Human in Outer space [closed]

Is it true that human in outer space can't differ right side and left side? Around human no another solid. Thanks.
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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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### 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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### 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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### 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. (p: D....
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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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### 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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### 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 ...
1 vote
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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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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