When it is said that G is true and unprovable it never means EXACTLY what it says.
— PL Olcott
What do you mean by this? Again, the ability to give a direct proof and something to be true are two different things. — ssu
So how can you prove this? Well, you prove it by reductio ad absurdum. So let's assume the opposite is true and hence statement S is provable and then go and prove that this cannot be. . Did you give a direct proof? No. You didn't prove S. You proved that not-S is false. — ssu
In mathematics, do you think there can be true, but unprovable statements? — ssu
But we do! We can give an indirect proof. — ssu
In mathematics, do you think there can be true, but unprovable statements? — ssu
It is exactly your fault, Olcott. By my count through at least 450 posts in good will and good faith made in an attempt to gain any clarity about what you are talking about, you have dodged, evaded, and avoided every attempt, content to make and repeat nonsense claims, and when pressed to change the subject.
Not a good look for you, and to my way of thinking making it impossible to have any respect for you. Sympathy? Maybe. Respect - which also implies trust - no. — tim wood
This isn't a particularly productive discussion. — fdrake
I am precisely focused on the central point from which this discussion is pursuant: — TonesInDeepFreeze
Whatever else the poster thinks he is doing, he claimed that classical logic is not truth preserving. I explained why that is false. The poster still refuses to understand the matter. — TonesInDeepFreeze
The poster lies that I believe that PA proves G or it proves ~G. It is the opposite. PA proves neither G nor ~G. That is the very statement of incompleteness. — TonesInDeepFreeze
The poster has to be bot. — TonesInDeepFreeze
Truth preservation is: If the premises are true then the conclusion is true. And that is PROVABLY upheld by classical logic. — TonesInDeepFreeze
Every expression of language X that is {true on the basis of its meaning} can only be verified as true on the basis of a connection to this meaning. — PL Olcott
What a seriously risible argument the poster makes! Really, the poster is as hopelessly ignorant, confused and irrational as they come. I've seen some that are more dishonest, but the poster ranks fairly high in dishonesty too, as just witnessed that he touts a Wikipedia article that actually shows the OPPOSITE of his own claim! — TonesInDeepFreeze
The poster said that G is untrue. Now he says he did not say it is false. — TonesInDeepFreeze
The Godel-sentence G is proven true in a meta-theory that is ordinary arithmetic. It is not at all controversial that in plain arithmetic the Godel-sentence is true.
It is completely a confused notion that G is false. — TonesInDeepFreeze
It looks very much like a case where how you're using the words, PL, is not how the literature is using them. And in that regard your ideas - as criticisms of the literature - are off target. — fdrake
The poster asks a question anew. He should read the post to which he is replying. — TonesInDeepFreeze
The poster cites "semantic connection". That is not a defined term. However, the semantics are clear, as I have mentioned over and over but the poster refuses to recognize: — TonesInDeepFreeze
Let CNC stand for "The cat is not a cat," intended here as a false proposition.
Let MGC stand for, "The moon is made of green cheese," also a false proposition.
Let K stand for the implication, (CNC => MGC).
According to the rules, K is true. Period. — tim wood
That is a basic result in sentential logic, known to anyone who has studied the subject. — TonesInDeepFreeze
If C is any contradiction and Q is any sentence, then:
C |- Q
That is a basic result in sentential logic, known to anyone who has studied the subject. — TonesInDeepFreeze
It's not a matter of the conclusion being false but rather that the poster previously tried to slip the discussion from the inconsistency of the premise to the falsehood of the premise. — TonesInDeepFreeze
Getting back to the poster slipping from the context of contradiction to falsehood: Yes, all contradictions are falsehoods. But not all falsehoods are contradictions. The point here is that mere falsehood is not what's involved in the principle of explosion. — TonesInDeepFreeze
If D is a contradiction, then M might be true or false. From the mere fact that D is logically impossible we do NOT infer that M is true. But the conditional D -> M is not just true, it is logically true. THAT is the principle of explosion and it does NOT imply that M is true. — TonesInDeepFreeze
And model theory adheres to the ancient notion of entailment: A set of premises entails a conclusion if and only if there are no circumstances in which all the premises are true but the conclusion is false. — TonesInDeepFreeze
The principle of entailment goes very far back in the history of logic. It is in model theory that the principle is given mathematical exactness. The model theoretic version adheres to the general principle: A set of premises entails a conclusion if and only if there are no circumstances in which the premises are all true but the conclusion is false. — TonesInDeepFreeze
It was claimed in this thread that most philosophers believe it is not the case that there are sentences that are true on the basis of their meaning.
What is the basis for that claim? — TonesInDeepFreeze
A contradiction doesn't make a false statement true. No one disagrees with that. And it is not the principle of explosion. — TonesInDeepFreeze
Given C, a contradiction, the expression C => P is true. That is because C is false, and whenever the antecedent is false, the implication is true - them's the rules. But it is an elementary and serious error to suppose this shows that P is true. For P to be true, C must first be affirmed. That is, C ^ (C => P) => P, C being true, affirms P. And this is exactly - or should be - what Tones said. — tim wood
* If C is any contradiction and P is any sentence, then we have C -> P, but that does not allow inferring P. Rather, we would infer P from (C -> P) & C. But since we never have C, don't have (C -> P) & C so we still don't have P. — TonesInDeepFreeze
(1) We know that "Not all lemons are yellow", as it has been assumed to be true.
(2) We know that "All lemons are yellow", as it has been assumed to be true.
(3) Therefore, the two-part statement "All lemons are yellow or unicorns exist" must also be true, since the first part of the statement ("All lemons are yellow") has already been assumed, and the use of "or" means that if even one part of the statement is true, the statement as a whole must be true as well. — PL Olcott
↪PL Olcott You're incoherent, here. And it looks like you do not understand the distinction between valid and true. — tim wood
↪PL Olcott Do you understand that in terms of these discussions and your replies to me you're talking crazy - most of your replies being either or both nonsense and non-sequiturs? — tim wood
Rather than merely bandying Richard Montague, the poster would do well to start at the beginning with symbolic logic as presented in his textbook: — TonesInDeepFreeze
You ether cannot or will not answer it. You describe what you call a set and make certain claims about it. You have not shown that it exists or can exist, or how it's built, and you certainly have not shown how it can satisfy the claims you make for it. — tim wood
* 'entailment' and 'consequence' are usually taken as specifying the same relation. — TonesInDeepFreeze
* If C is any contradiction and P is any sentence, then we have C -> P, but that does not allow inferring P. Rather, we would infer P from (C -> P) & C. But since we never have C, don't have (C -> P) & C so we still don't have P. — TonesInDeepFreeze
* Montague semantics is based on compositionality as with the method of models (though with extended aspects such as types, modality, intensionality and possible world models). — TonesInDeepFreeze
the set of expressions of specified semantic meanings
— PL Olcott
Please define this. If it is a constructed set, please show how it is constructed. — tim wood
The meanings of sentences are given by the method of models — TonesInDeepFreeze
The principle of explosion adheres to the principle of truth preservation. — TonesInDeepFreeze
The principle of truth preservation is: All cases in which the premises are true are cases in which the conclusion is true. Put another way: There are no cases in which the premises are true but the conclusion is false. — TonesInDeepFreeze
On may reasonably propose an alternative formalized logic, but a formalized logic requires that we have a purely mechanical method by which to determine whether a given finite sequence of sentences is or is not a proof, which requires a mechanical method by which to determine whether a given sequence of symbols is or is not a sentence. — TonesInDeepFreeze
And I've granted R all day long. But you're not talking just about R, but generalizing your claims beyond R, and as you persist beyond reason, so with reason I call you out and warn against engaging with you. And not to be forgot, you have been asked about R itself and given no answer. That is, R does not exist and I suspect cannot exist, either way, how is R an "ultimate foundation" of anything? By contrast, Godel et al were exactly rigorously clear about what their system(s) are. — tim wood
For a given language, we have different models. A model is an interpretation of the meaning of the symbols of the language. Per a given model, every sentence receives exactly one of the two truth values. That is, per a given model, no sentence is both true and false, and every sentence is either true or it is false. — TonesInDeepFreeze
Simplest is this: if P is undecidable, then neither P nor ~P are provable in R. I don't know what R is, but let's assume it stands for the kinds of systems that are actually relevant to this discussion, and which include arithmetic as described by Godel. As such, for clarity let R = G, and let us refer to P as unprovable in G. — tim wood
Simplest is this: if P is undecidable, then neither P nor ~P are provable in R. I don't know what R is — tim wood