# Questions tagged [logic]

Use this tag for general questions about logic that are not categorizable under some more specific tag, like "mathematical logic", "informal logic", "classical logic", etc.

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### Differentiating an argument from authority from expert testimony

Consider the following argument : The mathematical theorem T is a true theorem, because person(s) P say so. In a scientific context, it would be a fallacious argument from authority. However, suppose ...
376 views

### Computable syntax

It will be easier if I present the motivation in order to express the question better. Creating shorthand symbols for long sentences/propositions/assertions is ubiquitous. Many authors do it ...
1 vote
27 views

### Is it consistent with beginning/ending principles for an interval-based temporal logic to cover a time that is exactly ω+ω intervals long?

The SEP article on temporal logic reports on possible beginning/ending principles for instant-based temporal logics: beginning: ∃x¬∃y(y≺x) end: ∃x¬∃y(x≺y) Note that ≺ is the prior-to relation, here. ...
1 vote
225 views

### Translating a sentence with a time element into first order logic

The sentence I want to translate into FOL = "Some people lie sometimes" I know that Ex(Px ^ Lx) = "Some people lie" And Ex(Tx) = "There exist some times" (or "...
1 vote
126 views

### Logical Meaning of Apostrophe in Formal Notation?

In Allison Hills' paper "Moral Testimony" in Philosophy Compass, she refers to: i) p and ii) p'. This is in the context of discussion one's ability to reason about p and q such that one can: ...
297 views

### Are Gödel's Incompleteness Theorems a refutation of Rationalism?

According to Putnam, Gödel's theorems show that the set of truths in Number Theory (i.e., true propositions involving natural numbers and their properties) is not recursively enumerable, whereas all ...
1k views

### Is it possible for truth to be set by humans?

Let's say I create a video game. Let's call it V. Then I set a rule in V that you need to find a car in the game and click on it to jump. Now we ask the question of how to jump on V. Someone replies ...
863 views

### Trying to understand reality lead to understanding useless things?

If one sets his purpose as achieving the truest possible understanding of reality (I know one might die and not achieve it), then doesn't this mean that he needs then to understand all the things that ...
208 views

### Which philosopher proved that propositions cannot be neither true nor false?

Where can I find a comprehensive discussion of the idea that some propositions are neither true nor false? I know of Łukasiewicz but his discussion seems rather limited. Which philosopher if any tried ...
153 views

### Who first said: "Never deny, seldom affirm, always distinguish"?

In the context of medieval scholastic disputations, what is the origin of the axiom "Never deny, seldom affirm, always distinguish" ("Numquam negare, raro affirmare, semper distinguere&...
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### Is free will a third option aside from chance and necessity?

The determinism dilemma is that if our actions are predetermined they are not free, and if they are random they are not willed, either way there is no free will. Even if will causation is a mixture of ...
55 views

### How is Goldy related to the lady? [closed]

The question in concern that I'm trying to solve: Introducing a lady in party Goldy told her friend, “She is sister-in-law of my only brother who is father of Ganesh who is grandson of Navya’s ...
395 views

### Reference request for the definition of logic

I am looking for philosophical texts on the question of what the definition of logic is or should be. I am pretty sure many logicians and philosophers have written about that philosophical topic. I ...
340 views

### Mutually contradictory but simultaneously correct

In continuation of Two competing theories that are logically inconsistent my second question is there can be a theory/framework which can be interpreted in many mutually contradictory but ...
101 views

### Did what I do in this game constitute a logical fallacy or not?

Thinking about my previous question, I'm starting to think I didn't ask the right question. I'm making this to determine if I did or not. I don't think this is the typical type of question that goes ...
217 views

### What type of fallacy is used here? [closed]

For the sake of argument,Let us say some special group of people use definition of masculinism as "raising voices for Equality between men and women", One fine day, A Man Busy on mobile ...
71 views

### Hume's Guillotine

I struggle to understand how logic doesn't validate the deduction of a moral judgement that's not present in the first premise, even if we add a second premise? I might not be profound upon the matter,...
1 vote
178 views

### Can’t we assume that the Boltzmann Brain scenario can be cognitively stable?

In the Boltzmann Brain scenario, we are all brains produced by random fluctuations within a high entropy universe. The argument which I had accepted before was that our very reasoning can not be ...
1 vote
200 views

### Did i Just found the solution to radical skepticism?

If someone uses the premise that: 1=1 and then arrives at the conclusion that: 1=2 this means that the conclusion has proven the premise wrong; and if the premise is wrong, then the conclusion is ...
1 vote
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### How can one refute this argument that claims to do away with omniscience as a divine attribute?

Definition of omniscience: X is omniscient = for the whole preposition P, X knows the value of P. Let T be the set of all true propositions. An omniscient being knows all these propositions (T). Let ...
86 views

### Does space behave like a logical operator that applies rules to its elements?

I am asking due to being inspired by the following: Consider a particle system with uniform motion in vacuum not sensitive towards fluctuations, such that classical mechanics applies. Now, consider ...
1 vote
230 views

### Why is "the present king of France is bald" considered false?

Why is "the present king of France is bald" considered false? Because "present" means "existing" so it's paradocixal. Because the concept of "the present king of ...
245 views

### The enunciation clause (Lyotard & Levinas)

As kind of introductory remark, let me state that I'm not academically-trained in philosophy, so my apologies if this comes up as a rather simple question. I was reading Logique de Levinas by JF ...
108 views

### Is there a philosophical or mathematical proof for "For any observation or claim, there's an infinite number of assumptions we presume to be true?"

Is there a philosophical or mathematical proof for "For any observation or claim, there's an infinite number of assumptions we presume to be true?" It doesn't seem to make any sense, but ...
1 vote
55 views

### Why did Ayer consider every existential proposition synthetic?

....For, since existence is not a predicate, to assert that an object exists is always to assert a synthetic proposition.... What about math objects? If I say that the triangle with two angles exists,...
6k views

### Is God either amoral or not omnipotent?

The usual (Christian) justification for suffering/evil in the world created by a benevolent God is freedom of the will. However, the more interesting question is not about the source of evil (which ...
5k views

### Why do we prohibit consensual incestuous relationships?

When talking about sexual relationships between brothers and sisters, our initial intuition might be, “Well that’s just wrong. There’s something immoral about that”. Now, to examine the logic, I ...
1 vote
225 views

### Can premises be proven true if they lead to true conclusions?

Suppose that we have a bunch of premises which are unproven, but lead to a valid conclusion. Are the premises therefore valid?
2k views

### Do premises need to be valid conclusions?

I recently purchased "A Concise Introduction to Logic" by Patrick Hurley. I have a concern: if premises must be valid conclusions, can we ground truth on anything? Using an example from the ...
142 views

### How can you know if premises are true?

In logic, you start with premises to obtain conclusions. But how do you know that the premises themselves are true?
1 vote
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### Is it possible for a premise to be both tautologous and contradictory? [closed]

Is it possible for a premise to be both tautologous and contradictory? If it is possible, how so?
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### Do premises need to be true?

In logic, you start with premises that lead to a conclusion. Can you start a logical argument with premises that are not true?
136 views

### ls elementary mathematical equality essentially a self-identity statement?

In a lot of places equality is defined that for two expressions A=B, A=B means that A and B have the same value (A=B). This relationship seems strange as we are slightly abusing use/mention, if '=' ...
5k views

### How did first-order logic come to be the dominant formal logic?

Early formal systems like Frege's Begriffsschrift or Peano's work on the axiomatization of the natural numbers used axiom systems with an underlying second-order predicate logic (from today's point of ...
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### What type of logic notation would be best suited for pre-socratic arche expositions?

I want to formalize a few premises pertaining to Heraclitus, starting with the mundane and veering into the more advanced. The ἀρχή is fire Therefore, for all things x, their origins are traced to ...
622 views

### 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 ...
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### 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 ...
99 views

### "Present king of France" as a typical case of material implication

So why can't I consider "The present king of France is bald" as material implication? P = 'There's a present king of France', Q = 'A present king of France is bald'. Therefore "P -> ...
1 vote
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### Is there a meaningful difference between Aristotle's reasoning through induction and reasoning through example in chap 23-24 in prior analytics?

Aristotle presents reasoning through induction and reasoning through example as two different methods in chapters 23 and 24 of the Prior Analytics. He claims that induction is valid on the grounds ...
253 views

### Are these introductory logic textbooks wrong to teach ‘unless’ = ‘or’?

Colin Fine answered on Unless" does not equal "or" 'directly and intuitively'. This contradicts the textbooks beneath. Who is correct? Let me ask this here, as I prefer answers from ...
1 vote
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### What is the difference between temporal logic and Dialectical Logic (Hegel)?

I have been reading Hegel's Science of Logic where he critiques its generation understanding of logic known as Formal Logic. As I have come to understand one of the main differences between Hegel's ...
164 views

### How to motivate ‘unless’ = ‘if not’, with etymology?

My high school students still reckon Lande’s two motivations for ‘unless’ = ‘if not’ (below) too abstract, formalistic! Thus I need a third, but simpler, motivation with merely etymology. But how do I ...
2k views

### What's an intuition for material implication?

The paradoxes of material implication show that the usual interpretation of implication as "if ... then" statements leads to counter-intuitive results. For example, from (P & Q) -> R we can ...
160 views

### By what generic method do we correctly determine that an analytical expression of language is true?

The answer to this is a philosophy of logic question would seem to unify the notion of analytic truth across all formal and natural languages. This subject of this question seems to refer to the ...
1 vote
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### A question on contrapositives and predicates

So I am a freshman taking an intro class to logic. And the question started off from a class exercise we've got which asked us to identify the covering generalization for the following conditional ...
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### What is an explanation really?

Let's consider a hypothetical 'Church of the Moon' on a distant planet with a huge moon. The members of this church base all their beliefs about the moon and their religious practices on their holy ...
243 views

### What is the modality of a statement that follows from a necessary statement?

Let □P. Suppose □P => Q. What can be said about the modality of Q? □P <=> P holds in every possible world. Thus it is available as a premise to derive Q in every possible world. Suppose Q is ...
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### Is dialetheism falsifiable?

I was reading an article on dialetheism and the liar paradox and i came across an interesting comment. The writer said that dialetheists may accept the law of non-contradiction just for the sake of ...