Tagged Questions

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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63 views

Can a “real” paradox exist?

Given a statement, S: "S is not true." We arrive at a paradoxical solution whether or not we assume S to be true or false. Does this automatically imply that we have made an error in logic, ...
2
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1answer
35 views

How to start studying philosophical logic?

As I'm planing to study Philosophical logic, I've some important questions. For example, I wonder: 1-Should I start with the algebraic approach? Should I start with another approach?(which one?) 2- ...
2
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1answer
31 views

How to discharge an assumption?

I am proving the follow argument [(A ↔ B ) → C] ⊢ [ - ( A ^ B) V C ] Using the following set of rules I, ^E, vI, vE, →I, →E, ↔I, ↔E, --E, -I Here are my steps but I got to the point where I ...
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1answer
24 views

What are the names, or arguments of the atomic sentence “Max ate a cake” and “I ate a cake.”

What are the names, or arguments of the atomic sentence Max ate a cake and I ate a cake. ? First of all, "Max" is definitely a name. But is "cake" a name? And in the second sentence, is ...
2
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1answer
60 views

Logical Consequence and Tarski's World

I found this question in an old exam paper. I have no idea what is expected from a question like this. Consider the Tarski's world below. This world illustrates that ¬∃xTet(x) is NOT a logical ...
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1answer
72 views

Help with a proof for the following arguments

I want to proof the following argument from both sides using the following rules ^I, ^E, vI, vE, →I, →E, ↔I, ↔E, --E, -I Argument [(A ↔ B ) → C] ⊢ [ - ( A ^ B) V C ] Please let me know ...
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2answers
215 views

Is it possible to provide a proof of the following arguments?

G & ¬ H ¬ H ⇒ H Therefore, S & I Is it possible to prove the validity of this argument without having any information of S or I in the premises? H ...
2
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5answers
69 views

Question regarding sound argument

Sound argument is an argument which is both valid and it's premises are true. But my question is, why do we mention in the definition of the sound argument that "it's premises are true" when we've ...
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1answer
41 views

Proof validity methods other than truth tables

I have read or heard some time ago that truth tables cannot be used to validate arguments which involves the use of quantifiers i.e. in predicate or quantificational logic where you can find ...
2
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4answers
125 views

Must infinity involve repetitions?

Infinity for Nietzsche in at least one line of argument involves the eternal return; he refers to it in the Die fröhliche Wissenschaft and Also sprach Zarathustra; most completely in his Notes on the ...
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2answers
62 views

Method to derive conclusions

Suppose, you have been given the following assumptions: 1. (W ⊃ (F ∨ M)) 2. ~F 3. (M ⊃ A) In what way you can come up with conclusion from this? What kind of inferences rules can be used here? I ...
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6answers
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Climate change statement - is there a logical fallacy here?

"97% of scientists agree that climate change is caused by humans - if 97% of scientists told you a plane was going to crash, would you get on it?" Arguments about the existence of climate change ...
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1answer
62 views

Did Wittgenstein say something about intuition for logic?

When one creates some logical content, like in programming, only naives think that this is a rational way of thinking. In fact, this is based on patterns and intuition. Did Wittgenstein say anything ...
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3answers
40 views

Introductory Natural Deduction Question

So I'm new to logic and taking an introductory logic course, and I'm really having trouble with these 2 questions: Using the system of Natural Deduction in the textbook, provide a derivation to ...
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3answers
61 views

What is the logical connectives of Then?

What is the Truth Table Analysis of the below argument? If a football is more demanding than tennis and John is good football player, then John can become a good tennis player.But if football is ...
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3answers
119 views

Understanding why Quine thinks certain belief sentences are meaningless

According to Quine, the following sentence is literally nonsense: ∃x (Ralph believes that x is a spy) Question: Exactly how does the sentence above devolve into non-sense according to Quine? ...
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3answers
137 views

How does one contradiction in argument makes the argument valid?

For any argument such as the following that we solve by "Proof by contradiction" method: (A v B) (A ⊃ C) (B ⊃ D) [ Therefore, (C v D) Assumption: ~(C v D) Therefore, ~C {from 4} Therefore, ~D {from ...
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3answers
137 views

Logic - 3 Cannibals Riddle Reduced to 2 Steps

From reddit Cannibals ambush a safari in the jungle and capture three men. The cannibals give the men a single chance to escape uneaten. The captives are lined up in order of height, and are tied to ...
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5answers
118 views

Invalid arguments with true premises and true conclusion [duplicate]

I'm am study some classical logic and I am having trouble with argument validity. I learned to think of validity as determined by the definition "If the premises are true, then the conclusion must be ...
2
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1answer
79 views

Is there a name for a “You benefited therefore you did it” fallacy?

When talking about conspiracies, you often hear things like group X benefited from event Y therefore group X must have caused event Y I'm sure everyone knows lots of examples: 9-11, ISIS, ...
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0answers
30 views

Does anyone know of any essays on Adam's Thesis and Deontic Conditionals?

I'm curious if anyone knows of any essays which concerns how deontic conditionals fit with Adam's Thesis. (Adam's Thesis is the idea that the probability of an indicative conditional A > C is equal ...
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4answers
104 views

Why is the Kochsche Curve and programming so similiar? [closed]

I've question which I'm looking for longer time. The iteration process while a for loop > for statement in function_declaration: is looping over all instances and giving out one statement after ...
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0answers
58 views

Help with understanding the rules about Categorical Propositions in Syllogism [on hold]

Guys Can u help me with my Homework in LOGIC about Categorical Propositions? Example: All humans are mammal. (TRUE) CONTRADICTORY- Some humans are not mammal. (FALSE) CONTRARY- No humans ...
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1answer
49 views

Using natural deduction rules give a formal proof

With exams just around the corner I am really struggling with formal proofs. Using natural deduction rules give a formal proof of Q from the premises (¬P → Q)∧(R → ¬Q) ¬Q → ¬S ¬S → (R ∧ ¬P) So the ...
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2answers
57 views

Anyone can help me with natural deduction?

~(AvB) ㅡㅡㅡㅡ ~(BvA) I have to provide a derivation to establish validation of this argument. First of all, Can i first change ~(AvB) into ~A&~B by using de-morgans? And second is ...
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4answers
137 views

Does a beginning imply an ending? (In regards to the universe)

In regards to the universe if it said to have a start (Beginning) does that imply that it will have an end? Are beginning and ends implied when either ones is said to be true of a proposition or can ...
1
vote
1answer
36 views

How to stop thinking on reasoning? [closed]

I think I always think on the base of reasons and logically, but relations have problems with Reasons and Logic. Like if we Trust some one, we should do without demanding the explanations. is it a ...
2
votes
2answers
93 views

Where does Quine say logic should have no ontological presuppositions?

I'm sure I recall Quine saying in various places that one distinction between logic and set theory is that logic should have no ontological presuppositions (or, at most should presuppose some thing ...
0
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1answer
50 views

Modus Ponens and Modus Tollens Symbolic Proofs

I need a symbolic step by step proof to show me the validity of Modus Ponens and Modus Tollens. And someone please define the validity of a particular argument for me, because as I know, the valid ...
2
votes
4answers
92 views

logical form of the definition of validity

my text book gives the definition of validity as "An argument is valid IFF if the premises are true, then the conclusion must be true". Using a conditional elimination on the RHS of the IFF yields "An ...
3
votes
2answers
137 views

How could it be that the following sentence is NOT a proposition?

Consider the sentence "It might be dark outside". Is this a proposition? What sorts of arguments could you make that this sentence isn't a proposition? Is it that it is making -- potentially -- a ...
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1answer
23 views

What does it mean to “conditionalize a probability distrubition”?

What does it mean to "conditionalize a probability distrubition"? In case relevant, I've been reading about "Adam's Thesis", and that's where this phrase has been thrown about.
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3answers
112 views

Conditional disjunction equivalence proof using FItch

Prove P v Q ⇔ ¬Q → P So far I have the obvious things... 1. P v Q _ | 2. ¬Q | _ | 3. | 4. | 5. | 6. | 7. | 8. P 9. ¬Q → P → Intro 2-8 I think the problem here is that I do not ...
0
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0answers
40 views

An logical expression and its meaning

I will use an example sentence from Russell, so let W represent the predicate “... authored Waverley “ then (x)(Wx → (y)(Wy → y=x)) would express the same thing as the sentence 'At most one person ...
2
votes
1answer
176 views

Are there any other branch of mathematical philosophy?

Are there any other branch of mathematical philosophy? I am refer to the mathematical logic, are there any other branch of mathematical philosophy? For example, philosophical graph theory would be ...
9
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10answers
394 views

How could our universe suddenly appear out of nothingness?

How could our universe suddenly appear out of nothingness? I understand that the big bang created all things but how could it when nothingness is purely the absence of everything?
8
votes
4answers
181 views

Understanding Grice's Theory of (Non-Natural) Meaning

I am trying to understand Paul Grice's famous essay "Meaning". So consider a computer system which is fed a dictionary of every English word in existence. The computer system then randomly spits out ...
3
votes
2answers
86 views

The basics of anti-propositionalism

Anti-propositionalism -- as I understand it -- is the view that sentences don't express propositions. But if everyday sentences (like "The dog is behind the curtain") don't express propositions, what ...
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3answers
98 views

“Proposition” vs. “The Meaning of a Proposition”

Do the terms "proposition" and "meaning of the proposition" mean the same thing? Put differently: let P denote a proposition. Do the terms P and "the meaning of P" mean the same thing? Do they ...
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1answer
55 views

Are we spending too much time asking hard to answer questions while we'd be better off asking more productive ones?

I've heard this on several occasions and I think it is true if we're spending too much of our time on them. It might not be true for some people, but then, how do they decide it isn't true for them? ...
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1answer
99 views

How does free will defense of God's benevolence work?

The purpose of the defense is to show that omniscient, omnipotent and benevolent God is consistent with the existence of evil in creation. The most popular version of the defense is due to Alvin ...
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0answers
61 views

Testing the validity of syllogism argument

I came across a validation method for testing the validity of a syllogistic argument which seems quite easier to grasp: For example: To test the argument: no P is B some C is B Therefore, some ...
9
votes
5answers
288 views

Is God either immoral or not omnipotent?

The usual (Christian) justification for suffering/evil in the world created by a benevolent God is freedom of the will. However, the more interesting question is not about the source of evil (which ...
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1answer
46 views

Equivocation Fallacy: When the context of similarity is not the context of the argument

I often hear or read statements that seem to have a similar type of fallacious reasoning about it. I want to know if there is a name this type of fallacy: Top women chess players have a lower draw ...
2
votes
2answers
154 views

Logic Riddle, need help answering

I have attached below a propositional logic riddle that I am having difficulty solving. It would be great if one of you could post a solution to this problem with some clear and concise explanations ...
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4answers
110 views

What is the proper name for the group comprising “must” and “must not” (see disambiguation below)

In logic (or philosophy) jargon, what do you call the generalization of the two mutually exclusive condition states must and must not? I assume mustness isn't the correct term but it conveys what I'm ...
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1answer
84 views

The existence of unknown propositions? [on hold]

My question may seem strange and nonsensical for some, therefore I will try to explain myself to the best of my ability. So to make it clearer what I mean with my question. I will start by quoting ...
3
votes
1answer
84 views

Syllogistic Logic: Negation of a Categorical Proposition?

I am beginner of logic, and am writing an introduction to logic for a math book. I am of the impression that the three main areas of logic to explain are (in order) syllogistic logic, sentential ...
4
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6answers
117 views

Morality of God and Kant's Refutation of the Ontological Argument for God's Existence

I have in my discussions on religion made the comment that to discuss the bad (or perceived bad) properties of a God(s) for the unbeliever is not good logic as a thing must first exist before we can ...
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2answers
111 views

What is the difference between intensional and extensional logic?

Homotopy type theory talks is conjectured to be the internal language of (infinity,1)-toposes; it comes in two flavours: extensional and intensional - these aren't notions that I've come across before ...