Questions tagged [validity]
The validity tag has no usage guidance.
84
questions
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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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1answer
60 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 ...
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2answers
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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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0answers
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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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1answer
50 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)
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1answer
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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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3answers
105 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 ...
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4answers
272 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 “...
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4answers
325 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 ...
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2answers
140 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 ...
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2answers
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).
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2answers
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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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3answers
175 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 ...
3
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5answers
542 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, ...
2
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4answers
647 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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3answers
259 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 ...
2
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2answers
119 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 ...
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4answers
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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: ...
2
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2answers
68 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 ...
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5answers
2k 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!
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2answers
583 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
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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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1answer
61 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 ...
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2answers
230 views
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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1answer
69 views
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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5answers
171 views
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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3answers
161 views
Concerning the definition of “valid”
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 access without a strong basis in logic. Now I've taken ...
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3answers
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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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3answers
1k views
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 ...
2
votes
1answer
232 views
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
2
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2answers
103 views
Are valid arguments content blind?
Piggy backing off of this post here I want to make sure I understand this point clearly.
Are valid arguments content blind?
Even if the conclusions they make contradict?
For example, the following ...
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3answers
541 views
Can p and q in modus tollens be stated negatively?
In a youtube video a commentator summarizes Andrew Klavan's argument as
the following:
If God does not exist, there are no objective moral values.
There are objective moral values.
God exists.
The ...
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3answers
2k views
In basic logic, if an argument contains a self-contradictory premise, how come the argument is valid?
I have started to attend the logic lectures. The lecture notes indicate that a "self-contradiction" is a statement that is always false.
But why will it lead to a valid statement?
4
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4answers
364 views
Reverse Conclusion of Hypothetical Syllogism
I am presented with an argument of form:
If p, then q.
If q, then r.
Therefore, if r, then p.
Does this structure have a specific title? I know that it is invalid, and am assuming that "reverse ...
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0answers
105 views
What are the Limitations and Vulnerabilities of Objectivity Biases?
How reliable is a "Logic / Objectivity" Bias when it comes to reasoning? Or, What are the potential limitations or vulnerabilities of relying solely on these bases of reasoning?
Note 1: &...
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3answers
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Are “All A is B” and “If A then B” always logically equivalent?
Will "All A is B" always imply "If A then B?"
If so, can we say that the following follows the form of Modus Ponens?
All dogs are mammals.
Toby is a dog.
So, Toby is a mammal.
Can I rewrite ...
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5answers
3k views
Can you make a valid inference invalid by adding extra premises?
From An introduction to formal logic by Peter Smith there is a question:
Can you make a valid inference invalid by adding extra premises?
I think it's true. If I add premises that contradict ...
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1answer
141 views
Tautologies and Quantification
Are the following two questions a) tautologically valid, b) logically valid but not tautologically valid, or c) invalid.
Here's what I have so far:
For 10.3: It is not tautologically valid since the ...
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1answer
355 views
Soundness of a deductive argument
I am a student who was just introduced to philosophy.
On a test, we were given the following multiple-choice question on soundness of a deductive argument:
“Anything that travels in time necessarily ...
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1answer
525 views
Is it valid to prove the axioms of a system from themselves? How does it square with Gödel's incompleteness?
I recently asked whether the axioms are tautologies, and got comments that seemed to me highly suspicious. Namely, that you can always prove an axiom from itself, that you can trivially say A ...
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1answer
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327 views
Logical analysis of “Free will and god(s)” argument
Please evaluate the following argument strictly for formal logical validity. I am NOT interested in debating the content or in philosophical perspectives on the content. However, I AM interested in ...
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0answers
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What is a faster method other than truth tables for validating a sentence?
I've learned how to do truth tables with the different syntaxes (conjunction, disjunction, etc.), but when it comes to 3-5 atomic sentences it takes too long to do a full truth table with 8-32 lines. ...
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0answers
137 views
In the context of debate centred on a statement, how to validate arguments given to confirm or disconfirm that statement in a logical manner?
Let's say we have the following statement to serve as a starting point around which a debate can be centerd.
Man is immortal
Someone could say that man is mortal according to accepted scientific ...
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2answers
39 views
Not sure if my logical equivalences are correct here or not
I have a problem here that I'm trying to solve. The question asks me to check whether the argument is valid or not without using a truth table. I used equivalence laws to reduce the statement down ...
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1answer
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How to infer ¬Q when there seems to be no way to
Rule #1: No man shall hit another man.
Rule #2: If someone breaks Rule #1, then Rule #1 does not apply to such a one.
My specific question is: How can someone infer that Rule #1 does apply to him?
...
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7answers
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Is the logic of this argument valid?
If God exists, it is rational for people to believe he exists without relying on facts:
If God exists and he wanted to be known by people he would provide a
means of knowing him.
If God wanted as ...
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4answers
317 views
Does this philosophical argument about accidents and universal origin contain valid logical structure?
I'm not enough of a philosopher to properly analyze this particular argument, but I'm curious about it and I'd like to see it dissected and explained.
"If the solar system was brought about by an ...
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5answers
852 views
What fallacy dismisses a conclusion because supporters give invalid arguments for it?
A person dismisses an otherwise valid argument, because some of its proponents support it for the wrong reason.
How is this fallacy called?
EDIT: Here is an example. A person defends the idea that ...
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1answer
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Why must the sentence form of a valid argument be tautological? [closed]
I was thinking along the lines of the obvious, such as when found tautological the form must have been valid but I'm sure there is a more in-depth explanation that I can't reach.
