Questions tagged [logic]

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

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166
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16answers
44k views

Is 'guns don't kill people, people kill people' a good argument?

I'm hearing the argument X doesn't do Y people do Y in quite a few guises. For instance in it's original form guns don't kill people; people kill people Presumably, therefore guns are OK cars don't ...
81
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10answers
13k views

Is Kurt Gödel's Incompleteness Theorem a “cheap trick”?

I found a throw-away critique of Kurt Gödel's Incompleteness Theorem in an essay about Deconstruction: The basic enterprise of contemporary literary criticism is actually quite simple. It is based on ...
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12answers
17k views

Can you prove anything in philosophy?

I don't understand philosophy very well, and so I am wondering whether you can "prove" anything in philosophy. It always seems you can go a layer down, and find another question, almost endlessly ...
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6answers
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Logical fallacy: X is bad, Y is worse, thus X is not bad

I have heard this type of argument too many times: You are criticising X using well researched facts and arguments. Your interlocutor, states that Y is much worse with equally well researched facts ...
59
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21answers
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Is the “omniscient-omnipotent-omnipresent” definition of God consistent?

God is commonly defined as an omniscient (infinite knowledge), omnipotent (unlimited power), omnipresent (present everywhere) entity. Is there any logical inconsistency in this definition? I have ...
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13answers
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Does Pascal's Wager contain any logical flaws or fallacies?

Blaise Pascal's famous wager was that even if the existence of God cannot be determined through reason, a rational person should wager as though God exists, because living life accordingly has ...
45
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9answers
12k views

Why do I accept some inconsequential claims as “obviously true” without evidence? E.g. “Most people don't like to be hit on the head with a hammer.”

There are certain claims that I accept as obviously true without (much) evidence. For example: Most people don't like to be hit on the head with a hammer. Donald Trump ate dinner some time last week....
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16answers
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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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10answers
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What fallacy in Pascal's Wager allows replacing God with the devil?

I wanted to know the name of the fallacy or fallacies the Pascal's Wager in the sense that it can be applied to motivate one's belief in many things. A similar argument to the original Wager can be ...
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16answers
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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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17answers
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Why doesn't philosophy have higher standards for its arguments?

Mathematical systems are an excellent model for organizing and conducting thought: In the mathematics community, any argument in support of a conjecture, that deviates from "sound argument" never ...
36
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11answers
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Is it a fallacy if someone claims they need an explanation for every word of your argument to the point where they don't understand common terms?

Is it a fallacy if someone claims they need an explanation for every word of your argument to the point where they don't understand common terms? For example, suppose someone said, "If a dog bites ...
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10answers
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Is it a fallacy, and if so which, to believe we are special because our existence on Earth seems improbable?

People often use the argument that there must be a God, for example, because Earth and the laws of physics are perfectly situated for humans to exist the way we do. However, if Earth or even the ...
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12answers
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Is circular reasoning always a fallacy?

Suppose the following dialogue: ... "I accept only one notion of land property. Namely, 'I am doing my stuff here, therefore I am here". "But this means," he responded, "you ...
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13answers
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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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6answers
9k views

Three statements that contradict each other

In formal logic, it seems that a contradiction only arises between two statements. Is it possible to have a set of three statements that together are a contradiction, but where any two of the ...
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3answers
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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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3answers
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Is First Order Logic (FOL) the only fundamental logic?

I'm far from being an expert in the field of mathematical logic, but I've been reading about the academic work invested in the foundations of mathematics, both in a historical and objetive sense; and ...
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9answers
23k views

What is the difference (if any) between “not true” and “false”?

A fairly simple question I hope someone can help me with.
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3answers
3k views

How is Gödel's incompleteness theorem interpreted in intuitionistic logic?

Classically, one sets up an axiomatic system with a formal deduction system & an interpretation in a model. Generally it is sound, that is: a formally deduced theorem is also true when interpreted ...
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5answers
8k views

Is “I cannot imagine a mechanism for X to happen, so X can never happen” a named logical fallacy?

I have encountered this reasoning quite frequently: Somebody posits the hypothesis that an event X can happpen. A recent example I encountered was "vinegar and salt in the boiling water make eggs ...
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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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10answers
235k views

What is the difference between Fact and Truth?

I'm curious about the difference between Fact and Truth. I was searching on the internet if I could find it. But still I'm confused about the exact meaning. I first read the forum discussion here Fact ...
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10answers
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Isn't the notion that everything will occur in an infinite timeline an example of the gambler's fallacy?

I've seen a few different formulations of this, but the most famous is "monkeys on a typewriter" - that if you put a team of monkeys on a typewriter, given infinite time, they will eventually produce ...
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16answers
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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 ...
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3answers
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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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4answers
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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 ...
24
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7answers
5k views

What type of rhetorical device is the offering of a source which is really long and not specifying what part of the source is relevant?

I'm encountering a frequent recurrence of a rhetorical device that seems to me fallacious but I can't figure out what it's called. When making an argument, the person does the following: Makes a ...
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12answers
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How is gun violence comparable to drunk driving?

I just read "Is 'guns don't kill people people kill people' a good argument?" and it reminds me of another argument. I would like your opinion on whether or not it is a good argument. Gun Control ...
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10answers
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Can an argument be valid even though one of its premises is false?

Is it possible for an argument to be valid by virtue of its logical form, but contain a false premise? In other words, can a premise be false even though the argument itself is logically valid? ...
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3answers
18k views

What is modal logic for?

I understand "pure" logic as a structural description of what a valid proof is but I have never understood the reasons for using modal logic. What's an example typical of how modal logic is used?
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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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10answers
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Is it a fallacy to say that a sane person cannot apply rational thought to the motivations of the insane?

A common argument in today's news is that: Someone commits a heinous crime by shooting a bunch of people. Anyone who commits a heinous crime must be insane. Sane people cannot apply rational thought ...
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6answers
9k views

How is the argument “I love all logic, but I don’t love deductive reasoning. Therefore, the moon is made of green cheese.” valid?

This example came up in class: I love all logic, but I don’t love deductive reasoning. Therefore, the moon is made of green cheese. I understand the premise is contradictory and the conclusion ...
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10answers
6k views

Why can't humans believe contradictions?

I'm reading something on the topic of logic and one of the exercises asked me to convince myself that a contradictory statement was true. I could not convince myself of this and now I am curious about ...
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10answers
3k views

Are different values of nothing equivalent?

Are different values of nothing equivalent? Is 'no tigers' the same as 'no zebras'?
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12answers
2k views

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 ...
22
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12answers
4k views

Are there any philosophy books for an intelligent nine-year-old?

I would like to buy some books on philosophy for the child of a friend. He is very intelligent and mathematically able and clever for a nine-year-old. I remember near that age really enjoying the idea ...
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2answers
8k views

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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10answers
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What formal logical systems “resolve” the Liar Paradox?

Short version of my question. What formal logical systems can represent, and seem robust against, the Liar Paradox? N.B. I would like to avoid reference to truth-values, except inasmuch as they ...
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11answers
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Which fallacy: “If white privilege exists, why did Elizabeth Warren pretend to be an Indian?”

I recently came across this meme. It's clearly a logical fallacy (the existence of one use of a socioeconomic tool other than white privilege does not preclude the existence of white privilege), but I'...
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8answers
7k views

What fallacy is this? “This happened, therefore there must be good reasons for it”

What fallacy is it when someone says "this is true/it happened, therefore there are good reasons for it"? For example: We drive on the left (or right, depending on country) side of the road, ...
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6answers
39k views

What is the difference between a statement and a proposition?

I'm doing a MOOC on mathematical philosophy and the lecturer drew a distinction between a proposition and a statement. This is very puzzling to me. My background is in math and I regard those two ...
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7answers
5k views

Selection of logical connectives {¬,∨,∧,⇒,⇔} in set theory?

Nearly every treatment of set theory, whether Paul Halmos' Naive Set Theory, Herbert Enderton's Elements of Set Theory, Patrick Suppes' Axiomatic Set Theory, etc. introduce a common set of logical ...
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9answers
30k views

What is the difference between “necessary” and “sufficient”?

What is the logical difference between something being necessary in order for something else to be true; as opposed to something being sufficient to make something else true. i.e. Fuel is sufficient ...
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3answers
12k views

How is First Order Logic complete but not decidable?

Why doesn't completeness imply decidability for first order logic? First order logic is complete, which means (I think) given a set of sentences A and a sentence B, then either B or ~B can be arrived ...
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6answers
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Is infinite regress of causation possible? Is infinite regress of causation necessary?

For a number of reasons — including perhaps a desire to feel that we have a complete understanding of where we came from, or at least an understanding which is completely sufficient for all of ...
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1answer
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How can we reason about “if P then Q” or “P only if Q” statements in propositional logic?

When you have a propositional sentence of the form P ⊃ Q  — which we might read as "if P, then Q" — how can you tell when it is true, or false, based on the truth-values of P and ...
19
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5answers
9k views

Why does “Daisy has four legs” not entail “Daisy has more than two legs”?

I have been going through one of the books and I found an example of conclusion C that is not entailed by a premise P. Daisy has four legs. So daisy has more than two legs. Surely though, the ...
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10answers
3k views

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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