Questions tagged [logic]

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

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4
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1answer
579 views

What are the differences between hypothesis, supposition, assumption, postulate, and axiom?

What are the differences between hypothesis, supposition, assumption, postulate, and axiom?
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God's paradoxes and their implications [duplicate]

Possible Duplicate: Is the definition of God consistent? As many of you, I've come across a few paradoxes of all sorts, from logic to math, linguistics and so forth. Some of such involve God or, ...
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4answers
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Argument “a is b” but “b is not a” valid?

Is it true that in logic "a is b" but "b is not a"? Does it work one way or both ways? For example: a is b Therefore, b is not a If this is valid, How can you prove?
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192 views

Can knowledge about argumentation be sufficient for philosophical logic without too symbolic or mathematical concepts?

The most important element for expression of truth is trough an argument, with premises and conclusion. Argumentation requires to avoid fallacies and adhere to the truth. However logic if treated as a ...
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3answers
305 views

Can all mathematical reasoning be translated into traditional logic?

Can all mathematical reasoning be translated into traditional (Aristotelian, syllogistic) logic? It would seem not ∵ one cannot syllogistically establish the validity of the reasoning in the ...
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3answers
145 views

Material conditional: Why does the absence of the predicate validate the conditional? [closed]

So yeah, basically from what i've read, and i've checked multiple sources on this, is that A -> B = ¬A V B. So to really see where the confusion lies, I'll first state where it doesn't. Where A -> B, ...
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5answers
521 views

Shouldn't statements be considered equivalent based on their meaning rather than truth tables?

Consider the following truth table, which serves to define the logical connective ⇔, P | Q || P⇔Q T | T || T T | F || F F | T || F F | F || T According to the above truth table, the logical ...
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6answers
942 views

Is “Don't blame me; I voted for ___” a bad argument?

Is there a fallacy in the argument, "Don't blame me; I voted for ..."? Or is a voter's entire responsibility for their contribution to whatever current state of political affairs they experience ...
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3answers
369 views

Are truth-claims inappropriate?

Strictly speaking, is it inappropriate to make a truth-claim? I am seeking an answer from Philosophy (Epistemology), and feel free to use logic I am speaking "theoretically", not "practically" I am ...
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7answers
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Is it possible to be truly unbiased?

I was pondering this question: Inductive Argument Against Believing Anything I his argument, the OP suggests that, in the position of choosing a system of belief where there are multiple, large ...
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2answers
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Aristotle's Syllogistic and Proofs by Contradiction

I'm just reading about Aristole's work on syllogism in Anthony Kenny's A New History of Philosophy book. I'm struggling to understand the tranformations between different forms of syllogisms. So ...
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1answer
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Are Univalent Foundations of mathematics a modern version of logicism?

As I understand it (and mine is just basic understanding) the Univalent Foundations program is an attempt to reduce mathematics to an interpretation of Martin-Löf type theory by using homotopy theory....
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Are we are born with some innate sense of critical thinking or is this simply the product of an education? [closed]

I was listening to some young children in my family the other day talking to each other. The one Nephew told the one Niece. Only boys play with cars to which the she replies well then my sister is a ...
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In formal logic, how is it possible for an argument with a contradictory conclusion to be valid?

I've recently been trying to introduce myself to formal logic, and I've hit a stumbling point: In the text I'm reading, a valid argument is defined as "an argument in which it is impossible for the ...
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7answers
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What logical fallacy is the argument “I have a RACE_NAME friend, so I can't be racist”?

What logical fallacy is the argument "I have a RACE friend, so I can't be racist"? For example, some people will make this point when trying to defend a comment they made: PERSON A: "I think all ...
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1answer
201 views

name this fallacy: A was P in the past -> A must be P now

I've been seeing arguments of this form for awhile: (agreed true premise) Some predicate P was applicable to behavior/event/thing A in the past. Variations: P(A) may have been true at some particular ...
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4answers
226 views

Is it possible to deny that language necessitates ontological commitments?

I am unsure of what I am trying to put my finger on, but it seems like it is an enormous assumption that ontological commitments can be - or should be - necessitated by simply the language that we use....
4
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1answer
374 views

What did Wittgenstein (mean to) achieve in the Tractatus?

I read the Tractatus about a decade ago, and was impressed, both by it and I suppose myself! But suddenly I'm seriously wondering what the book has or could achieve. Not so much how it changed ...
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3answers
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What fallacy argues that we should do nothing because we can not do everything?

A says to B "we should recycle because it is better for the environment," and person B says "if we wanted to be better environmentally, there's lots of things we could do that we don't, so we shouldn'...
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4answers
805 views

How can a tautology not be necessarily true?

My logic/philosophy exercises include the following statement: "Every tautology is knowable a priori but not every tautology is necessarily true." I'm bamboozled. How can a tautology not be ...
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3answers
615 views

What does the truth-value of a material implication represent?

This question comes from my attempts to understand what the truth value for a material implication with a false antecedent represents. I have seen several justifications for this convention, usually ...
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2answers
373 views

Can strong omnipotence be decomposed into logically possible and logically impossible aspects?

A lot of debate in the "omnipotent being" or "omnipotent, omniscient, omnipresent, omnibenevolent, etc." being debate revolves around the definition of the terms. I consider the "strong form" of ...
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1answer
838 views

What is 'major' about the major term in logic? [closed]

Source: p 264, A Concise Introduction to Logic (12 Ed, 2014), by Patrick J. Hurley Each of the three terms in a categorical syllogism has its own name depending on its position in the argument. ...
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3answers
117 views

How does philosophy advance despite irreconcilable background assumptions (“positions”) on every topic?

In philosophy there are always, and on almost everything, many "positions", many different possibilities to choose from, and there isn't mainly some decisive conclusion between positions as to what's "...
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3answers
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How do we know that if the statement “A → B” is correct, “¬B → ¬A” is correct?

All examples that I can come up with confirm that If "A → B" is correct, "¬B → ¬A" is correct, but is it possible to rigorously prove that negating a true implication always will result in another ...
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4answers
665 views

What is wrong with my intuition of Modus Tollens?

Abbreviate Modus Tollens to MT, Necessary Condition to NC, and Sufficient Condition to SC. I pursue only intuition; please do not answer with formal proofs or Truth Tables. I already know of the ...
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5answers
740 views

Are all sufficient conditions necessary?

If X is the necessary condition of A, then it doesn't follow that X is sufficient. However, if X were a sufficient condition, would it also follow that X is a necessary condition? Put otherwise, is a ...
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3answers
601 views

What is the term used for logic statements which are non reversible?

Something along the lines of If A then B, if B then not. A has to be true before B can be true but if B is true first then A isn't true. Is there a term describing this in logic or philosophy?
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3answers
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How can you intuit that P → Q ≡ ¬P ∨ Q, and not P ∨ ¬Q?

As I forgot to stipulate the pretermission of the logical equivalence P → Q ≡ ¬P ∨ Q here, some of the answers presume this and resemble petitio principii, and so are really proofs rather than ...
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2answers
527 views

Is the real number line actually real when we construct it?

Intuitionism is akin to constructivism in mathematics but not quite the same from what I can tell. In the usual treatment of the real line, the additional numbers are found between the rationals by ...
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1answer
233 views

What is the intension of the concept “intension”? [closed]

I think that it should be possible to assign to all concepts a plausible intension, consisting of just one or two words. However, in textbooks or encyclopedias I never found such focused appointments ...
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1answer
65 views

Can different varieties of modality be used with existential quantification?

I'm wondering if it makes sense to talk about worlds which aren't this one being real. It seems like you can claim that something possibly exists. Now I'm wondering, because it seems to amount to ...
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4answers
241 views

What is the fallacy that privileges one person over another?

I see this a lot, someone in a category of people attempts to shut down anyone with an opinion that is not from the same category. For example, people without children weighing in on parenting; the ...
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0answers
131 views

Is it there any trivialist model in physics (like in quantum mechanics)?

Trivialism is a system that proposes that literally every proposition is true and false at the same time blatantly breaking the principle of no contradiction and triggering the principle of explosion (...
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1answer
256 views

Why does Zeno's paradox seem valid but remain obviously wrong?

Look at this argument: The 1st introduction: We may present time on an axis; therefore any time interval is a segment, thus consisted of infinite number of points, on this axis. The 2nd introduction: ...
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1answer
296 views

Is it really problematic for Universal Instantiation to precede Existential Instantiation?

Abbreviate: Existential Statement to ES, Existential Instantiation to EI, Universal Instantiation to UI, and Universal Statement to US. Source: A Concise Introduction to Logic (12 Ed, 2014) by ...
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4answers
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If-then in propositional logic [duplicate]

Possible Duplicate: How can we reason about “if P then Q” or “P only if Q” statements in propositional logic? Here's the table for If-then _____ ___________ | A B | (A ⊃ B) | | 0 0 | 1 ...
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1answer
71 views

How to intuit 'unless'? [closed]

I already know, and so ask NOT about, the proof of: A unless B =  A if not B =  Either A or B. Because I ask only for intuition, please do NOT prove this or use truth tables. My problem: I want to ...
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0answers
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Can hypercomputation compute the impossible?

There are things which are illogical/logically impossible (like saying that 2+2=4 and 2+2=5. Without changing anything in the axioms of mathematics or logic, this would be a contradiction and would be ...
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2answers
212 views

Language proof and logic Chapter 15 question 16 help

I'm trying to go about solving this problem but I'm having problems even knowing how to approach it. Can someone help me to set it up? Here is the premise: ∀x∀y(x ⊆ y ↔️ ∀z(z ∈ x ⟶ z ∈ y) Here is ...
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1answer
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Vacuous Conditionals and How We Feel About Them

Let's take the following propositions : 1 - "If Bill Gates is poor then Bill Gates is rich". 2 - "If Bill Gates is poor then the moon is made of cheese". Both propositions are inevitably true ...
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Can two different objects at the same time be the same? [closed]

Can two things be different and yet the same at the same time? For example, a chair (white) does not have one leg and another (black) has all of its legs. As in the question, these two things with ...
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Is First Order Logic (FOL) the only fundamental logic?

I'm far from being an expert in the field of mathematical logic, but I've been reading about the academic work invested in the foundations of mathematics, both in a historical and objetive sense; and ...
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15answers
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Is there any rigorous philosophical basis for atheism?

Definition/Update In what follows I use the term God to refer to an entity that has at least one of the following properties: Has created the universe Is omnipotent Is omniscient Approaches to ...
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9answers
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What is the difference (if any) between “not true” and “false”?

A fairly simple question I hope someone can help me with.
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Difference between implication/conditional and logical entailment?

What is the difference between the implication/conditional truth function and the notion of logical entailment? My naive understanding as a computer programmer is that the conditional is a function ...
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9answers
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What fallacy in Pascal's Wager allows replacing God with the devil?

I wanted to know the name of the fallacy or fallacies the Pascal's Wager in the sense that it can be applied to motivate one's belief in many things. A similar argument to the original Wager can be ...
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Is the claim “this coin is fair” falsifiable?

Wikipedia says, The claim "No human lives forever" is not falsifiable since one would have to observe a human living forever to falsify that claim. Thinking on similar lines, even if the ...
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7answers
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Has quantum mechanics destroyed the fundaments of logical reasoning?

In quantum mechanics it is thought to be possible that something could be at two places at the same time. But if that is really the case then perhaps law of non-contradiction is no longer valid. So ...
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10answers
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Are different values of nothing equivalent?

Are different values of nothing equivalent? Is 'no tigers' the same as 'no zebras'?