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Can an argument be valid even when its premise refutes the conclusion? (Trying to disprove my professor)

I want to ask about something that I saw in philosophy class today. Let's say that this is a valid argument, and let's call it argument A: Premise 1: P1 Premise 2: P2 Conclusion: C And there's ...
femboy420's user avatar
2 votes
1 answer
68 views

Precise definition of valid argument using model theory

In philosophy 101, I learned that a valid argument is any argument that satisfies this property: if all of its premises are true, then its conclusion must hold true. Now, I am taking a class on ...
Jimmy Yang's user avatar
7 votes
3 answers
241 views

Is an argument with contradictory premises valid?

I have hard time determining whether the below argument is valid: (P1) Nobody ever plays with a bear. (P2) Bob plays with a bear. (C) Therefore, bears are friendly. I think this argument is valid. ...
John Davies's user avatar
0 votes
0 answers
24 views

Is Validity or Justification Always Valuable?

Although it is debatable that justification is a necessary or sufficient condition for knowledge, many philosophers make the claim that it is. African-American philosopher of culture Alain Locke ...
Paradox Lost's user avatar
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3 votes
1 answer
88 views

Good reasoning vs necessary truth-preservation vs validity

On pages 19-20 of Logic: The Laws of Truth, Smith argues that "good reasoning" cannot be equated with the properties of necessary truth-preservation (NTP) or validity on the following ...
user51462's user avatar
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1 vote
1 answer
116 views

What is the difference between a tautological corresponding conditional and (P v ~P)?

The Wikipedia article on the corresponding conditional contains the following sentence: An argument is valid if and only if its corresponding conditional is a logical truth. Some sources use "...
user51462's user avatar
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0 votes
5 answers
466 views

Is there an infinite amount of things that are not present?

Sitting here at my desk, there is not a bottle of meth. There is not an elephant. There is not a car. There is not a unicorn. There is not a salad. There is not a cat. There is not a dog. There is not ...
I divi's user avatar
  • 17
0 votes
2 answers
75 views

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. ...
Maverick's user avatar
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5 votes
2 answers
670 views

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 ...
user107952's user avatar
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2 votes
3 answers
525 views

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: &...
Chris's user avatar
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2 votes
3 answers
69 views

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 ...
jimboweb's user avatar
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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 ...
Name's user avatar
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0 answers
298 views

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 ...
Abdul Muhaymin -Free Palestine's user avatar
0 votes
1 answer
117 views

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 ...
part-two's user avatar
2 votes
5 answers
621 views

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....
John Smith's user avatar
-1 votes
1 answer
148 views

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 ...
part-two's user avatar
0 votes
3 answers
211 views

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 ...
part-two's user avatar
0 votes
1 answer
124 views

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 ...
user107952's user avatar
  • 7,046
-1 votes
1 answer
173 views

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 ...
sixo33's user avatar
  • 7
2 votes
4 answers
133 views

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 ...
danBeginner's user avatar
1 vote
1 answer
200 views

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’. ...
User1265's user avatar
2 votes
1 answer
56 views

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. ( ...
Floridus Floridi's user avatar
0 votes
1 answer
177 views

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 ...
Sazzad Hissain Khan's user avatar
0 votes
2 answers
70 views

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 ...
Sazzad Hissain Khan's user avatar
1 vote
1 answer
798 views

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 ...
Not a Salmon Fish's user avatar
1 vote
3 answers
769 views

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. ...
Not a Salmon Fish's user avatar
1 vote
2 answers
193 views

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 ...
Ninch's user avatar
  • 35
2 votes
1 answer
117 views

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....
farce's user avatar
  • 21
0 votes
1 answer
505 views

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 ...
user8616916's user avatar
4 votes
5 answers
427 views

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://...
Speakpigeon's user avatar
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1 vote
0 answers
132 views

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 ...
nbogs's user avatar
  • 159
1 vote
1 answer
127 views

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)
Grandene's user avatar
1 vote
1 answer
152 views

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 ...
nbogs's user avatar
  • 159
2 votes
3 answers
156 views

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 ...
Borut Flis's user avatar
2 votes
4 answers
2k views

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 “...
RaquelV.S.'s user avatar
2 votes
4 answers
370 views

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 ...
a.t.'s user avatar
  • 131
1 vote
2 answers
196 views

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 ...
Hierarchist's user avatar
1 vote
2 answers
5k views

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).
Micaela's user avatar
  • 59
1 vote
2 answers
99 views

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 ...
Micaela's user avatar
  • 59
1 vote
3 answers
518 views

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 ...
A. Delarge's user avatar
3 votes
5 answers
642 views

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, ...
A. Delarge's user avatar
2 votes
4 answers
989 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 ...
James Graham's user avatar
0 votes
3 answers
514 views

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 ...
user avatar
2 votes
2 answers
123 views

‘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 ...
ilovewt's user avatar
  • 175
3 votes
4 answers
18k views

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: ...
tarit goswami's user avatar
2 votes
2 answers
124 views

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 ...
Pedro A's user avatar
  • 206
3 votes
5 answers
5k views

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!
Curious 's user avatar
1 vote
2 answers
2k views

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
user avatar
22 votes
10 answers
15k views

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? ...
Curious 's user avatar
1 vote
1 answer
73 views

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 ...
mavavilj's user avatar
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