Stack Exchange Network

Stack Exchange network consists of 174 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

Questions tagged [logic]

For questions about logic, whether it concerns syllogistic logic, mathematical logic or the nature of logic itself.

0
votes
5answers
160 views

How do I operate with philosophers if I reject deductive reasoning?

Deductive reasoning is the one that takes premises for granted. I never do it. Therefore I never do deductive reasoning. Well, enough jokes. It is safe to assume that deductive reasoning never should ...
1
vote
4answers
184 views

How is “~A. Therefore A -> B” a valid argument?

I’m teaching myself logic from ‘Logic: The Laws of Logic’. In this book it states that 1) any sequence of propositions counts as an argument. 2) valid is when true premises of an argument cannot ...
4
votes
1answer
111 views

Do Alexius Meinong's impossible worlds describe all impossible worlds/things? [duplicate]

Does his impossible worlds category include (and can describe) literally all impossible things/worlds? Inconsistencies, paradoxes, impossible solutions to problems (and impossible problems); really ...
0
votes
2answers
126 views

Is this a paradox about clairvoyance?

You play a game with a fortune teller. There are two cards with the face down on the table; he wins if you raises the card's suit he foresees, you win if his prediction turns out to be wrong. Suppose ...
2
votes
1answer
67 views

Basic Logic: Arguments with Unnecessary Premise

Should an argument be considered invalid if there is an unnecessary premise? P1: A dog is a mammal. P2: All mammals have hair. P3: A dog is an omnivore. C: A dog has hair.
1
vote
1answer
57 views

Describing differences between “computational” and “non-computational” proofs

Is there a term that distinguishes proofs that can be performed by a straightforward computation related to the meaning of the proposition from proofs that build a tree of intermediate expressions ...
22
votes
6answers
8k views

How is the argument “I love all logic, but I don’t love deductive reasoning. Therefore, the moon is made of green cheese.” valid?

This example came up in class: I love all logic, but I don’t love deductive reasoning. Therefore, the moon is made of green cheese. I understand the premise is contradictory and the conclusion ...
1
vote
1answer
142 views

Derive |- [(P>Q)>P]>P using only primitive rules

I've been having issues trying to derive |- [(P>Q)>P]>P in natural deduction using only primitive rules. Wondering if anyone would have a solution to it. Thanks
1
vote
0answers
72 views

Why cannot the following theory be refuted by logic but is rejected because of lack of empirical support?

The following statements are taken from a book: The man in the street, and also the philosopher K. Marbe, believe that after a run of seventeen heads tail becomes more probable. This argument has ...
2
votes
1answer
41 views

Logic Either..Or

In the book: "Elementary Logic" authored by Brian Garrett, he has a few examples, one with solution and one without that conclude the following: 1) Either many people will attend the concert, or it ...
1
vote
1answer
77 views

Is Tarski's schema T trivial?

Tarski's schema T asserts that: (T) x is true if and only if p where x is the name of any sentence of the language in question and p is the expression which forms the translation of this sentence ...
1
vote
1answer
66 views

Is there a truth value for a predictive conditional?

Does a predictive conditional have a truth table value? I have this question because we can't check if the antecedent or consequent is true or false.
1
vote
0answers
56 views

Syntactic and semantic eliminability/conservativeness

Let L be a ground language, and L+ the extension of L with additional signature terms and axioms. We say L+ is syntactically conservative over L if every sentence in L that is provable in L+ is ...
1
vote
1answer
250 views

Is this passage about different reading speeds an argument?

The pace of reading, clearly, depends entirely upon the reader. He may read as slowly or as rapidly as he can or wishes to read. If he does not understand something, he may stop and reread it, or ...
1
vote
3answers
73 views

Basic Logic: Presuming Truth

Given my belief that X is false, is it still possible for me to agree that if X were true, then Y?
1
vote
2answers
346 views

Are the following statements necessarily true, necessarily false, empirically true, or empirically false?

All cats are animals. TV's did not exist before the 20th century. All bachelors who are married are both married and unmarried. What I think is the classification of each statement: Necessarily true....
1
vote
4answers
163 views

Is it possible to know the truth value of a statement without knowing any information about that statement?

Is it possible to know the truth value of a statement without knowing any information about that statement? If no, then to me that would imply that truth values are not absolute and depend on how we ...
1
vote
2answers
84 views

~(P&Q) derive to ~Pv~Q

I would be grateful if someone could derive, by showing the proofs that: ~(P&Q) derives to ~Pv~Q. The same derivation would be appreciated for |- [(P>Q)>P]>P
5
votes
1answer
142 views

What's the meaning of the meaning of life? [closed]

Let's say that the meaning of life is X (avoiding evil, fulfilling our desires, obeying God, fleeing the pain of the fear of the death, collecting turtles – anything). What is the meaning of X? Even ...
1
vote
3answers
89 views

Hypothetical syllogism

So hypothetical syllogism is: if a then b if b then c so, if a then c . According to wikipedia, "In short, it states that if one thing happens, another will as well. If that second thing happens, ...
3
votes
1answer
132 views

Can any logic system provide the impossible solution to Russell's paradox in naive set theory?

In naive set theory in classical logic, we cannot describe or find a solution to Russell's set paradox (it is impossible). But is it there any logic system or any method that can provide this ...
1
vote
3answers
107 views

Understanding hypothetical reasoning and material implication

I am a little bit frustrated in how we use hypothetical reasoning in everyday life. Many times we make "if-then" statements. For example, if i get ill ,then i cant go to work and if i cant go to work ,...
0
votes
1answer
104 views

Basic Logic: True Premises, False Conclusion?

Is possible to have a false conclusion given that all its premises are true?
3
votes
1answer
61 views

What to read for an introduction on the epistemology of logic?

I would like to read about the epistemology of logic, preferably at a undergraduate level (not being a philosopher myself). What (text)book should I read for a good introduction on these topics? The ...
1
vote
1answer
138 views

quantified propositional logic and predicate logic

I am curious if there is a system that allows for both quantification over first-order objects and quantification over propositions, and also has inference rules that allows one to infer from a first-...
-1
votes
2answers
65 views

Is there a scenario before the formation of the world? [closed]

Energy turns into hydrogen atoms, and then the stars are born.، So maybe there was a scenario before the formation of the world. Could this be a sign of a pre-designed scenario? Has this topic (the ...
0
votes
3answers
43 views

Implication vs sufficient condition vs hypothetical reasoning

I was bit confused to clarify the difference between them because "if-then" are used a lot in everyday life. So for example we have a car which is full function and someone says if i turn the key the ...
3
votes
2answers
64 views

What did C. S. Peirce mean by this remark about the phrase “necessary and sufficient condition”?

As I was reading through The Collected Papers of Charles Sanders Peirce, I came across the following sentence: I doubt not that readers have been fretting over the ridiculous-seeming phrase “...
2
votes
2answers
34 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 ...
0
votes
1answer
88 views

Is there any logical system/method where impossible/illogical/inconsistent things can exist (like a solution to Russell's paradox that makes sense)? [duplicate]

Discussing with a philosopher about impossible things existing or being allowed within a particular logic system, he told me: "This is a funny thing about logically impossible things. You can prove ...
5
votes
2answers
1k views

Is there an English language example where modus tollens is valid but contraposition is not valid?

I was reading an answer by Bumble where the topic of modus tollens being valid but contraposition being not valid came up: https://philosophy.stackexchange.com/a/43004/29944 More importantly, there ...
0
votes
1answer
75 views

Is “all truth is relative” an absolute truth?

All truths are relative, and this is the only absolute principle. wrote August Comte. Anyway a radical relativism poses a serious problem: if every truth is always relative, is the latter an ...
1
vote
0answers
49 views

syllogism, truth-functional, or neither?

I dreamed that John F. Kennedy was born in 1917, and everything I dream is true. Therefore, Kennedy was born in 1917. All horses are animals. Therefore, all heads of horses are heads of animals. If '...
2
votes
2answers
161 views

What is the difference between a conditional and material implication?

Can someone help me understand the difference between a conditional and a material implication? Both of them have the "same" (if-then) structure. For example, "if x=2, then x^2=4". Is this a ...
3
votes
4answers
560 views

Is being something and not any other thing a necessary and sufficient condition of existence?

Is being something and not any other thing a necessary and (the only) sufficient condition of existence? I'm working on something close to the idea of Apoha, but in an ontological sense. I suppose ...
2
votes
6answers
453 views

Agnostic theism and agnostic atheism and their validity

Recently, there has been a rise of the terms like "Agnostic Theism" and "Agnostic Atheism" which one rarely comes across in philosophical literature. To me, these terms seem more of a mockery of the ...
2
votes
3answers
154 views

Understanding the simulation argument

I came across Nick Bostrom's paper called Are You Living in a Computer Simulation?. The paper argues that at least one of the following propositions is true: The human species is likely to go extinct ...
4
votes
3answers
182 views

How do logicians think about Hegel's logic

I was told, a while ago now, that if I wanted to study Hegel, even Hegelian Marxism, I'd be best off studying his logic first. Having recently asked this question I was wondering how do contemporary ...
1
vote
3answers
60 views

If-then syllogism and multiple conditionals

Can one condtional statement cancel another one ? For example i say if you get 85/100 at maths test i will gift you a car a but if you get 85/100 at maths and 50/100 at history i wont gift you ...
2
votes
3answers
120 views

The Euthyphro Dilemma (complete philosophy newbie here)

I have never taken a philosophy course or even asked a philosophy question in my life, although I do have some experience with mathematics and some logic. So, permit me to ask a question that is not ...
2
votes
3answers
148 views

How to prove P ∨ Q : ~ (~P & ~Q) with natural deduction

Here's another Tomassi's problem I can't solve (Logic, Exercise 3.9.1.17, page 106): P ∨ Q : ~ (~P & ~Q) I have to use natural deduction and the only rules I know are: assumptions, modus ...
2
votes
1answer
63 views

For a clairvoyant able to perceive time as we perceive space, is the future determined?

We can think about a future event as unknown or not yet existing, but once it has happened, it can be only as it is. If I am in an instant of time t1 and in a subsequent instant t2 an event x occurs, ...
6
votes
2answers
802 views

Can paraconsistent or other logics make the impossible happen?

A paraconsistent logic system it is defined as "a logical system that attempts to deal with contradictions in a discriminating way. Alternatively, paraconsistent logic is the subfield of logic that ...
-1
votes
1answer
55 views

He hasn't found the false positive yet, but he is committing a logical fallacy. What is the fallacy?

I have a co-worker who is trying to tell me that his checksum test between objects is a sufficient test to see if they are the same. I am trying to explain that just because two checksums test the ...
1
vote
2answers
82 views

What is the purpose of showing our emotions? [closed]

What is the purpose of our showing emotions? showing our emotions isn't real (well somewhat), they are simulated by the brain because of hormones(in some cases) and they aren't needed and mostly over ...
2
votes
4answers
101 views

When someone responds to an argument by changing the subject, what fallacy are they using?

Assume there is a controversy about classification of a newly-discovered animal species. Professor A argues: if an animal has feathers, then it is a bird; this animal has feathers; therefore this ...
2
votes
3answers
158 views

Once it happened, an event was necessary?

What would happen to an event in the past, if time itself ceases to exist? Without time, has what existed (such as the writing of this sentence) never happened? A total disappearance of space-time ...
2
votes
2answers
183 views

What's the difference between philosophy and academic philosophy? [closed]

What's the difference between Philosophy and academic philosophy, simple, yet so complex? Philosophy is the act of studying reality, knowledge etc. Yet in academic philosophy, you aren't studying ...
3
votes
4answers
145 views

Has the universe no identity?

1) A thing has an identity if there's something else delimiting and defining it. 2) The universe (intended as the totality of things) has necessarily no identity, because being the totality of things,...
3
votes
3answers
491 views

Inductive and deductive arguments and mathematical induction

I started reading Paul Teller's A Modern Formal Logic Primer. In the first chapter, the book presents the inductive and deductive arguments with the following examples: The inductive argument: ...