Logic is the study of formal systems of reasoning, especially of the deductive variety. It is one of the few fundamental philosophical subdisciplines, along with metaphysics, ontology and aesthetics. Logic has taken on considerable importance in recent mathematical developments, and one of the ...

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How to justify the use of logic?

I would like to hear some Philosophical arguments which justify the use of logic. Additionally, if a justification of logic takes the form of an inference, this inference itself makes use of logic. ...
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1answer
74 views

Does judgement of character make sense in a predetermined system? [on hold]

As I tried to understand the believe in the Abrahamic God I have come up with this logical problem. If I understand correctly, after we die we will be judged by God according to how we lived our ...
3
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1answer
44 views

Do malformed propositions have True/False values?

Many people are familiar with the malformed questions that, no matter which way they are answered, reflect poorly on the person to whom they were asked. For example: Have you stopped beating your ...
-3
votes
0answers
42 views

What's the irony or joke: 'Sir. My knowledge is zero.'? [closed]

[Source :] One of my teachers told us how he had retorted to his own teacher at the end of a heated debate- [1.] Teacher [says]: So you think you know more than me? Son I have 1000 times the ...
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0answers
47 views

Solve Syllogistic logic proof without Conditional Proofs (PA-CP) or Reductio (PA-RAA) [closed]

Basically, solve using only replacement + inference rules Allowed to use: -- All replacement rules -- Conjunction Elmination/Introduction -- Modus Ponens/Tollens -- Hypothetical Syllogism -- ...
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2answers
67 views

First book to self-learn logic, mainly to improve reading comprehension?

I read Where is a good place to start reading about logic? and ask.metafilter.com, but want to focus on improving comprehension and parsing of difficult writing. I never studied logic before, and ...
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0answers
17 views

Which is a good book for learning (introductory) logic in the german language?

I need a logic book in the german language, preferably introductory rather than a focus on simbolic logic. The book should show how one constructs different sentence structures and how one expresses ...
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votes
1answer
56 views

Is this way of thinking about the differences between men and women valid? [closed]

Problem I think that there's a common message out there today driving women to think they need to be treated the same as men, and thus deny any mental differences, when the right word that needs to ...
2
votes
2answers
69 views

LPL Q6.26 without --> or material implication

This is a repeated question: Language Logic and Proof Q. 6.26 "Using the natural deduction rules, give a formal proof of A ∨ D from the premises A ∨ (B ∧ C) (¬ B ∨ ¬ C) ∨ D" The LPL textbook ...
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2answers
54 views

Sentential Derivation: Derive ~(RvB) from ~R and ~B

I'm having a difficult time deriving ~(RvB) from ~R and ~B. This would be fairly straight-forward if we were allowed to use the DeMorgan Laws, however my professor is not allowing us to use them for ...
6
votes
10answers
220 views

Does the imperfection of man imply the imperfection of God?

I'll begin by laying out some some ideas that are considered true for the sake of argument: 1. Given: God Exists 2. Given: God is Perfect 3. Given: Everything God does is good 4. Given: Everything ...
1
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1answer
51 views

Why is the darapti syllogism invalid?

I found the following exposition of darapti on wikipedia: All squares are rectangles. (MaP) All squares are rhombuses. (MaS) ∴ Some rhombuses are rectangles. (SiP) As far as I can see, this is ...
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1answer
52 views

Modal logic and Boolean algebras

Is there an intrinsic, hidden modal logic within ordinary (abstract) Boolean algebras? I do not question whether interior or closure algebras are Boolean algebras. Nor do I seek for an explanation of ...
1
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4answers
104 views

“This sentence is true”. Is there a word for this class of statement?

Is there a term that means "A self referential statement which is true if (and because) it is true and false if (and because) it is false"? "This sentence is a lie" is a paradox in the sense of ...
2
votes
0answers
96 views

Why killing/death is more accepted (morally) than nudity on television/movies? [on hold]

Is there any logic why killing/death is more accepted (morally) on television rather than nudity/sex? It seems like a paradox to me the fact that all the laws (in the Occident) have severe punishment ...
0
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2answers
107 views

If magic is “fake,” why is science real? [closed]

Consider this: I watch a Harry Potter movie when I am a kid (I did) and, as early as kids, of course, older people tend to teach young kids at some point that motion pictures are "fiction" and not to ...
0
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0answers
35 views

Philosophically (through logic and reason) how does one get to liberty, freedom, destiny from positivism--raw science?

Auguste Comte was so 'positive' that there could be no metaphysical system, no explanation of essences (no need for such in an 'enlightened' age). He thought citizens should be trained only to look ...
0
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2answers
50 views

How does negation operate in modal logic?

I was mulling over this proposition: Just because something is provable doesn't mean that it is important; and wanted to consider its contrapositive. How would I write this in formal (modal) logic? ...
2
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3answers
139 views

Help with a proof in CSL

Premise: (A implies B) implies C Conclusion: (C implies A) implies A I had a logic exam a few hours ago, and this was one of the problems, but I really didn't know where to start. Since the ...
2
votes
3answers
56 views

Is the following statement a fallacy?

You only X because you Y. (with Y being true!) Example: Paul only defends the drug decriminalization because he has never been aggressed by a drug addict. Is this a fallacy? If not, how can we ...
0
votes
1answer
33 views

Counter argument to Nozick's counter to principle of fairness

Are there any strong counter arguments of Nozick's counter argument to principle of fairness. Nozick argues that although people may receive the benefits from the state, it does not mean the people ...
0
votes
1answer
48 views

Is the phrase “logic and reason” grammatically correct?

I have always interpreted logic to mean a systematic form (premise-reason-conclusion) of reason. So it seems that you are saying one word (reason) and a branch of that word (logic). But the "and" ...
2
votes
4answers
130 views

Is it an ad hominem attack to call somebody a troll?

Case 1: Person A criticizes person B. Person B says "We shouldn't feed the trolls. Best not to engage." Case 2: Person A voices their opinion on an issue being discussed on the forum. Person B says ...
5
votes
3answers
617 views

Should I learn logic before learning philosophy?

I read this question (this is the most relevant I found) with the answers however I still don't have the answers to my questions. I started reading the first lines of some philosophy books, I ...
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2answers
130 views

What kinds of logic or philosophy to improve comprehension of difficult writing?

In this post, the answer uses some logic to simplify a convoluted sentence. What's that kind of logic called? What other branches of logic or philosophy should I self-study in order to help ...
1
vote
1answer
47 views

Transitive Incompleteness of Logical WFF's Due to Godel's Incompleteness Theorem

If a set of theorems, or wff's, are used in conjunction with one another, does this have an impact on their completeness in terms of soundness? For example, I have five theorems of logic, or ...
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votes
1answer
37 views

The logic behind whats considered artistic?

I'm trying to teach my skeleton to dance. 3d skeleton.. in a computer. The skeleton is controlled by an ai that exerts force on the joints. How each joint behaves is defined by a function, the only ...
0
votes
1answer
25 views

Use-Mention distinction with letters

When you spell a word, are you using or mentioning the letters? Also, in general, is it possible to use letters?
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2answers
46 views

How to show non consequence / logical consistency?

How would I show non-consequence with this set? I can't seem to figure out the significance of the Universal and Existential indicators here. (∀x)(∃y)Fxy (∃y)(∀x)Fxy and the other question i'm ...
0
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2answers
64 views

How to prove a theorem using Sentential Derivation

I have to prove that [¬ A → ¬ (A → B)] → A is a theorem using the rules of SD. Any hints or advice?
0
votes
3answers
61 views

How to derive ( E v C ) using sentential derivations?

I'm having a really hard time trying to derive (E v C) from {~A > ~B, A > C, B v D, D > E}. Where '>' is the material conditional, so that 'A > C' is read as "If A then C". I used negation ...
0
votes
1answer
42 views

Proof of a Conditional and Discharged Assumptions

Currently, I am self-teaching myself formal logic from E.J. Lemmon's Beginning Logic. So far, the book is discussing the rules of derivation for propositional logic, and I've struggled to fully ...
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2answers
182 views

Every argument is an instance of an invalid argument form

This was a question posed to us in a lecture. I have been thinking about it for ages. Can I say that since all argument are instances of this invalid form p => q, the statement is true?
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2answers
61 views

Subtly inconsistent axioms

It is not known whether widely used axiomatic systems such as ZFC are consistent and Godel has shown that it is not possible to prove that they are, at least within the system. In an inconsistent ...
4
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2answers
83 views

Logic and presentation

In this question I suggested that logic is almost only ever used in philosophy as a means to present an argument. By implication, I meant that every formal argument can be stated informally, and that ...
2
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1answer
58 views

Who invented the notion of Philosophical Zombies?

Philosophical zombies are beings that look like human beings, act like them, drink, eat, talk, and in every other way behaviorally identical to normal human beings. However they have no inner life. I ...
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3answers
94 views

'Can't answer' as a philosophical response to moral questions

On the Quora forum, there is a question called "Are Some People Better Than Others?" One answer contrasts an altruistic doctor with a selfish criminal, but concludes that there is no real reason to ...
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0answers
40 views

In Jain Logic what 'is' or 'can be' asserted to be true and indescribable?

Classically a truth value is asserted of a proposition: thus by its very nature it must be describable. Jain Logic has a 'truth value' which is asserted to be true and indescribable; by the above it ...
4
votes
7answers
187 views

What logical fallacy is the argument “I have a RACE_NAME friend, so I can't be racist”?

What logical fallacy is the argument "I have a RACE friend, so I can't be racist"? For example, some people will make this point when trying to defend a comment they made: PERSON A: "I think all ...
0
votes
1answer
34 views

How being unable to settle all disputes makes it possible to settle many disputes?

I'm reading Wieland's: Infinite Regress Arguments. In here: I don't understand how the fail to settle all disputes implies that one couldn't settle many of them. The only possibility I see is ...
1
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4answers
65 views

Is it a fallacy to claim someone is committing a fallacy without explaining why?

Making use of an argument about a subject X, Person 1 presents his view to Person 2. Then Person 2, who is against that position, simply makes the following claim: "Hey dude, you have committed the ...
1
vote
3answers
83 views

Logic Question: Symbolizing sentences that use “some”?

How would one go about symbolizing the sentence "some cats are black?" Would I use A: All cats are black and N: No cats are black, in the notation [~A & ~N] so as to say "It is not the case that ...
2
votes
1answer
117 views

Logic problem in TOEFL book

I came across the text about weather system So I think the passage infers that every chaotic system is subset of nonlinear equations weather systems are subset of nonlinear equations chaotic ...
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votes
2answers
47 views

Logic question: Is ~(P&Q) equivalent to (~P&~Q)? [closed]

Where '~' is the sign for naught, and stands for "it is not the case that". My question is, is "it is not the case that (P&Q)" equivalent to "it is not the case that P & it is not the case ...
3
votes
6answers
278 views

How can telling the truth amount to a lie? [closed]

According to the Sorites, all men have beards, they just vary in length, density and coarseness. In a loose sense, a beard must have some appreciable length to be considered a beard. Yet, how much ...
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0answers
51 views

Real in Mathematics Vs Real in Philosophy [closed]

Real is being really analyzed. The two subjects--Mathematics and Philosophy use the term Real. Is there any difference between these two Reals? How can we show their difference using Mathematical ...
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2answers
100 views

Is it possible to appeal to emotion without commiting a fallacy?

People often make arguments from authority, and not all of them are fallacious. If the given authority is an expert on the discussed field, if there is a consensus among the experts of that field, and ...
0
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1answer
54 views

What does Sartre mean with that existence precedes essence and how is it related to the earlier existential philosophers' thoughts?

What does Sartre mean with that existence precedes essence and how is it related to the earlier existential philosophers' thoughts? Existential philosophers like Kirkegaard, Heideggers and Friedrich ...
3
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8answers
597 views

Can there be an argument without premises?

After a lengthy discussion with WillO here, we can't seem to find a common ground and I am interested in whether there really could be an argument without a single premise. Another question whose ...
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1answer
39 views

If all the premises are true and the conclusion is false, is it possible for the argument to be logically valid? [duplicate]

Where an argument is logically valid "if and only if it is not possible for the premises to be true and the conclusion false." Are there any examples of a logically valid argument where the premises ...