Questions tagged [validity]

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The logic of analytic inferences

Consider the following argument: P1: A is a father. Therefore: A is a parent. The above inference is analytic and valid: it is impossible that someone is a father without also being a parent. ...
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Is there a definition of logical validity that does not rely on possible worlds?

The definition of a logically valid argument in most logic books is that an argument is valid iff there is no possible world where the premises are true and the conclusion is false. But this relies on ...
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Logic exercise (evaluation of whether an argument is valid)

Interested in others thoughts on the following logic exercise (from Peter Smith's Introduction to Formal Logic, 2nd ed., available for free at https://www.logicmatters.net). Here are the premises: &...
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Is there a term that means "soft validity?"

By "soft validity" I mean this: The formal definition of validity is that if the premises are true, the conclusion must be true. I will call this "hard validity." "Soft ...
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Proof of the Model Universe Theorem: Proving the invalidity arguments in quantifier logic

I am studying how to prove an argument in quantifier logic is invalid. The textbook I am using by Virginia Klenk claims that you can use a Model Universe that contains a finite number of objects to ...
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Proving validity/invalidity of a modal argument

□(A v B) → (□A v □B) ...(1) This symbolic argument is intuitively invalid. In (1), if we replace B with ~A, then we see that though the antecedent is necessary, the consequent is a contradiction since ...
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Does the "because" in a premise disrupt the validity of this argument?

One is good if and only if one does one's job well One does one's job well if and only if, and because, one is virtuous One is virtuous if and only if one is just From 1 and 2: One is good if and only ...
2 votes
5 answers
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How can syllogisms with contradictory premises be valid?

A syllogism is valid if it is impossible for the premises to be true and at the same time the conclusion to be false. Consider the following syllogism: P1: This apple is red. P2: This apple is not red....
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How to make this argument valid?

If Peter is virtuous, he manages a household with patience. If Peter is to be good, he needs patience. Here's my attempt to understand 1 and 2. I get confused by the wording and necessity-sufficiency ...
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3 answers
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Checking the validity of an argument

Is the following argument valid? If A is to be good, they must be just If B is to be good, they must be just Therefore, if C is to be good, they must be just Therefore, if C is just, they become good ...
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If this world is the only possible world, what does that mean for validity in logical arguments?

Validity is usually defined in terms of possible worlds. More specifically, an argument with premise set S and conclusion C is said to be valid if and only if there is no possible world with all the ...
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Can someone explain why this immediate inference is valid?

everyone. Thank you very much in advance for any help you can give me with this issue. I'm enrolled in an Introduction to Logic course, and we're currently working on Categorical Propositions. I've ...
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Deductively valid arguments and situations

In book 'Logic: A Very Short Introduction', Graham Priest has quote about deductively valid arguments. Here is one problem. Assuming that the account is correct, to know that an inference is ...
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1 answer
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Question of Validity in syllogisms of deductive argument

I read the following excerpt from my A-Level Philosophy book: "Two key terms that you need to understand in relation to deductions and other forms of argument are ‘validity’ and ‘soundness’. ...
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1 answer
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Valid or invalid? ( from a CSU Exam, instructor Tim Black)

Source : http://www.csun.edu/~tab2595/PRAC_EXAM_1.pdf Is the following argument valid or invalid? (1) No email messages are written carefully, (2) but every love letter is very carefully written. ( ...
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How can we prove this argument is invalid?

Let's say below is the argument, Premise 1: All men are mortal Premise 2: Socrates is a man ------------------------------------------ Conclusion: Therefore, Socrates can think Now, to prove an ...
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Is it a valid argument?

I wonder if the below argument is a valid or invalid? Premise 1: All the humans can fly Premise 2: I am a human --------------------------------- Conclusion: Therefore, I can fly I also wonder, if ...
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1 answer
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Is it true that if an argument is invalid, any argument of that logical form must be invalid?

I am stuck over whether these statements are true: First: "If an argument is invalid, any argument of that logical form must be invalid." Second: "There may be invalid argument with ...
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3 answers
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can an argument containing a contradiction be valid argument

I know that validity has nothing with truth of the conclusion or with how good argument is in general, and an argument is valid iff the truth of its premises guarantees the truth of its conclusion. ...
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Are there multiple definitions of validity?

I have recently started learning the basics of propositional logic. According to http://intrologic.stanford.edu/chapters/chapter_03.html, a sentence is valid if and only if it is satisfied by every ...
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Counterfactuals in Premises for Arguments

Can counterfactuals in premises make an argument sound and valid? I understand that soundness requires both validity and true premises whilst validity requires the premises to follow to the conclusion....
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In logic, can we or can we not prove that a formula is invalid?

I'm a novice in this field of logic. While reading about soundness and completeness of a method, I read this line: "a logical system has the soundness property if and only if every formula that ...
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Where is the fallacy in Seth Yalcin's counterexample to the modus tollens?

Where is the fallacy, do you think, in Seth Yalcin’s argument (2012) that the Modus Tollens is not a generally valid form of argument? Seth Yalcin’s counterexample to the Modus Tollens (MT) https://...
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Modal Logic: Proving Schema Validity

When faced with a question of the sort, "Is schema X valid in class of frames C?", we usually go about proving or disproving this by assuming the antecedent of X and showing that the consequent ...
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Is this an argument by simplification: it can be done by doing Y, therefore it can be done?

The problem is X This problem can be easily solved by doing Y Therefore this problem can be easily solved I am confused if this is Simplification (Which means the inference is Valid)
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Modal Logic: Why are Universal frames a subset of Equivalence frames?

I'm looking through the lecture notes for my course on modal logic and am having a hard time understanding why it is that U, the class of all Universal frames, is a subset of E, the class of all ...
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3 answers
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Why is there an O type conclusion in modus celaront

Modus celaront is type logical syllogism. No reptiles have fur. (MeP) All snakes are reptiles. (SaM) ∴ Some snakes have no fur. (SoP) The conclusion is of a O type(Some .. are not ...). Why is ...
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What is an argument with necessarily true conclusion?

I cannot understand what an argument is with a necessarily true conclusion. Could you explain to me what it is and write here some examples? Moreover, what is the meaning of “necessarily true” and “...
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4 answers
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Analogy between an unknown in an argument, and a contradiction in the principle of explosion

Context I like to argue that, since we do not know what consciousness is, we can not specify what it can not do. Therefore we can not state we can't do something now, nor in the future. Up to the ...
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Is this argument about ownership valid?

I came across an argument that I believe to be invalid: Ownership is defined as the ability to exclude others. "Everyone owns land" becomes "everyone has the ability to exclude others from land." I ...
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Is the following statement true, false, or can't be determined? Why?

"If it snows and we don't have school, then (x^3)<0 implies x is negative" (Assume x is a real number).
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I need some help determining the validity of the following argument

“I got the highest grade on the last test and I have perfect attendance. If I get a cold, then I miss at least one class. I came down with a cold. Therefore, if I missed at least one class, then I ...
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Is this argument about "either or" valid or invalid?

Unless something weird has occurred, either the basketball game is cancelled, the football game is cancelled, or Churchill never entered Switzerland. If any game is cancelled, then something weird has ...
3 votes
5 answers
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valid or invalid: “S or R. Not S and Not R. Ergo, B.”

“Either it is sunny or it is raining. But now, it is neither sunny nor is it raining. So, the Boston Bruins will win the Stanley Cup this year.” Is this argument valid or invalid? I’m pretty stumped, ...
2 votes
4 answers
862 views

Is this argument about abortion being both right and wrong valid or invalid?

Abortion is either right or wrong. If it is right, then people should be allowed to kill fetuses. Killing fetuses is wrong. Hence, abortion is not right. If it is wrong, then women won’t have the ...
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Arguments/premises to disprove God's omniscience

I was thinking about validity of God's omniscience and stumbled upon three statements, which can be summarized as - To be omniscient, a being would require to capture and store all the data in the ...
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2 votes
2 answers
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‘The claim that I had an affair with Miss A and that I didn’t father her child is false’

The prosecutor asks, ‘Did you father the child of the murdered victim Miss A?’. Mr. N replies, ‘The claim that I had an affair with Miss A and that I didn’t father her child is false’. In response ...
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Is "(1) All humans are mortal. (2) Socrates is mortal. Conclusion: Socrates is human." unsound argument?

I am new to a philosophy course and recently learned about validity and soundness of an argument. In this exercise: Premise 1: All humans are mortal. Premise 2: Socrates is mortal. Conclusion: ...
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2 answers
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Is it possible to define argument validity as a formula?

Let A, B and C be propositions. Define ARG(A, B, C) as the following argument: A. B. Therefore, C. My goal is to create a formula whose truth value is equivalent to "ARG(A, B, C) is ...
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Are all fallacious arguments invalid?

Is it possible for an argument that contains a fallacy to be valid? I have been told that fallacious arguments by definition are invalid. Is this true? Thanks!
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How do I prove: 1. A v (B & C) 2. (A v C) > ~(G & O) / ~G v ~O

This is a question for my philosophy. Prove this valid using any of the rules we've studied so far: A v (B & C) (A v C) > ~(G & O) / ~G v ~O
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22 votes
10 answers
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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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Can a priori reconsideration improve on a priori theory? "Analytical" etc. schools

So something strange I've realized lately, in the humanities and social sciences it's fairly common to see labels such as "analytical", "analytic school" etc. which I read to suggest as if these ...
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Why is Truth the default designated value in logic and language?

It seems that investigations of language and logic have focused on truth as the assumed designated value (the value preserved by valid entailments). It is only in later, non-classical logic that non-...
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Are these basic arguments considered valid and sound?

I'm trying to come up with some basic arguments to construct a philosophy paper and I am wondering if the following arguments are valid and sound. Thanks for the help! If humans have flaws then they ...
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Is university research a guarantee for accuracy of theory?

Is university research a guarantee for accuracy of theory? I think and speculate that no and on the contrary the "status" of academic degrees and university relationships are used to "validate" even ...
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What is the nature of "validity" in deduction when dealing with conclusions unrelated to premises?

I studying graduate math (not very far into it), and I realized that some of the higher-level math texts I would like to read are hard to understand without a strong basis in logic. Now I've taken ...
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If the premises of an argument CANNOT all be true, then said argument is valid

Based on the fact that a deductive argument is said to be valid if and only if it takes a form that makes it impossible for the premises to be true and the conclusion nevertheless to be false, I am ...
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Determine if an argument is valid or invalid

The following is an argument. Is it valid ? Abortion is not wrong, because women have a right to control their bodies. The following is also an argument. Is it valid ? All students love ...
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Question about validity of Modus Tollens vs. Denying the Antecedent

I have no idea why (2) is an invalid argument. (1) If A, then B Not B Therefore not A (2) If A, then B Not A Therefore not B