# Questions tagged [proof]

For questions about the correctness of a proof or the nature of proofs in general.

322 questions
Filter by
Sorted by
Tagged with
868 views

### I've confounded myself with this formal logic "proof" [closed]

Let "r" mean "it's raining" and "s" mean "it's snowing." "->" is "implies"; "V" is "or" (inclusive); "~" is "not"; "^" is "and" Here's the "proof": (1) (r->s)V(s->r) is true because it's a ...
• 129
1 vote
585 views

### What can suffice as a scientific proof for God? to what domain can such a proof belong to? [closed]

"Scientific" theories require proof, and there are certain guidelines and standards for the proofs to be acceptable to the "scientific" community in that domain (Algebra, Computer Science, etc.). ...
• 135
214 views

### Establishing Incompletenes of Modal LPC

In Hughes and Cresswell A New Introduction to Modal Logic (1996 ed.) page 271, they attempt to establish the incompleteness of the system K + G1 + BF (where K is L(P->Q)->(LP->LQ), G1 is MLP->LMP, and ...
• 175
441 views

### Negative facts and truths

I know Russell and Wittgenstein argued about negative truths. It is easy to prove the existence of some property provided there is considerable empirical evidence for its existence, but what if we are ...
• 370
2k views

### Origin of the idea that something can't be proved, only disproved

Does anyone know if the idea that something can't be proved, only disproved has a specific origin? I often hear it and would like to make a reference to it in a term paper I'm writing. Is it from the ...
• 43
728 views

### How to check if this proof is valid?

I'm having some doubt if this proof is valid or invalid, especially regarding the line 4 derived from line 2. Do I need to change the letter in there? 1. (z)~Fz ∴ ~(z)Fz Using Indirect proof ...
• 527
2k views

### Does Descartes prove that he isn't dreaming?

I had a midterm question where this was relevant, essentially it was: "Assuming you're an atheist, how would you prove to Descartes that your last vacation wasn't a dream?" I put that since ...
• 204
5k views

### Why is Modus Ponens valid?

I am having trouble understanding what defines Entailment operator. On Mathoverflow I posted this question on what I perceive to be paradox of entailment. Consider: Modus Ponens: P therefore Q P ...
• 426
3k views

### How to prove you are an atheist?

I've been reading a conversation between two individuals - A claiming to be atheist and B asking him to prove it, since B does not believe that A is saying the truth and can't be sure if A is really ...
• 293
909 views

### Are there any known deficits of "relevant logic"?

The principle of explosion is the law of classical logic and similar systems of logic, according to which any statement can be proven from a contradiction. Some early formal systems like Frege's ...
• 3,919
900 views

### Claims that we know (virtually) nothing - can they be refuted?

Here's an argument that I've heard a number of times from friends and on the Internet: "The ratio of what we know about the universe to what we have yet to discover is so small - it is therefore ...
210 views

### What is a mathematical or logical name for the process of proving a statement by exhausting the problem domain?

I am trying to understand logic and I came across a set of actions that I describe below that I can't get my head around. Suppose you have a bag of multiple colored balls. Situation 1. Argument: ...
• 143
388 views

### Underlying logical structure behind Descartes' Ontological argument?

Quoting SEP: Version A: Whatever I clearly and distinctly perceive to be contained in the idea of something is true of that thing. I clearly and distinctly perceive that necessary ...
2k views

### Is there something in the real world that cannot be proved nor disproved? [closed]

It is often said that you cannot prove nor disprove God. People who bring forward this kind of reasoning often try to persuade you that there is a kind of balance, a truce; you can't prove your point (...
• 1,033
522 views

### Does the law of excluded middle follow the law of excluded middle?

Example is that the word unknown is not unknown so it doesn't define itself. Similarly French is not French, it's in English, and "long" is not long and only 4 letters short. That's by example my ...
10k views

### Is illogical = not logical?

I think law of excluded middle makes sense to mean that a statement should be either logical or illogical but in this case I don't assume "not logical" = "illogical" since the author didn't say "...
848 views

### What does it mean that a claim is a claim of nonexistence?

This question has devolved into a discussion. As I understand the discussion, everything is revolving around the veracity of statement Nonexistence can never be proven. and on what exactly ...
19k views

### Does a negative claimant have a burden of proof?

I have often heard it said that the burden of proof is on the positive claimant but not on the one making a negative claim. A person claiming, "God exists" has a burden of proof but not a person ...
11k views

### What is the difference between "reductio ad absurdum" and "proof by contradiction"?

What is the exact difference between reductio ad absurdum and proof by contradiction? Wikipedia used to state that: Reductio ad absurdum (Latin: "reduction to the absurd") is a form of argument in ...
• 615
868 views

### Are there any potential flaws in the definition of validity as "provable or falsifiable"?

I have made an argument in another thread that a proposition must be provable or falsifiable to be valid. Are there any flaws in this definition of validity? What might be a potential counter-argument ...
• 1,550
332 views

### Are the limitations of language proof against the divinity of holy books? [closed]

Many religions like Islam and Hinduism have holy books(the Quran and the Vedas, respectively) which claim some kind of superhuman origin. However, are the limitations of languages then counter to ...
• 873