On 28 Feb 2011, at 21:37, benjayk wrote:

Bruno Marchal wrote:On 27 Feb 2011, at 00:25, benjayk wrote:Bruno Marchal wrote:On 23 Feb 2011, at 17:37, benjayk wrote:Bruno Marchal wrote:Bruno Marchal wrote:Brent Meeker-2 wrote:The easy way is to assume inconsistent descriptions aremerelyan arbitrary combination of symbols that fail to describe something in particular and thus have only the "content" that every utterance has by virtue of being uttered: There exists ... (something).But we need utterances that *don't* entail existence.If we find something that doesn't entail existence, it still entails existence because every utterance is proof that existence IS. We need only utterances that entail relative non-existence or that don't entail existence in a particular way in a particular context.You need some non relative absolute base to define relative existence.The absolute base is the undeniable reality of there being experience.But this one is not communicable. It does play a role in comp, though.But we can say "there is an undeniable reality of there being experience". Isn't this communicating that there is the undeniable reality of there being experience?OK. I was using communicating in the sense of a provablecommunication. You cannot convince someone that you areconscious. Ifhe decides that you are a zombie, you might better run, probably,butthere is no way you could prove the contrary.OK this makes sense. But is there any provable communication, then? Afterall we can never prove the axioms needed for a provablecommunication.All axioms are provable in one line. Just say "provable by axioms".Sorry, I don't understand you here. How does saying "provable byaxioms"prove anything? It seems to be a description of charateristic thatcaneither be true or false (provable or not provable by axioms). Probably you mean something else, but I don't know what.

I meant "provable by the fact of being an axiom".

`A proof is a sequence of formula, each of which are either an axiom or`

`a result from a previously proved formula by the means of the`

`inference rules.`

Let me give an example: The theory T has the following axioms: 1) p 2) p -> r 3) r -> u

`And the (common) modus ponens inference rule: it says that from a`

`formula A and a formula A -> B, you can derive the formula B`

In the theory T, it is easy to prove u.

`The proof is the sequence of formula, (I add justification alongside,`

`but formally they don't belongs to the formal proof)`

p (by axiom 1) p -> r (by axiom 2)

`r (by modus ponens and the two preceding formula in`

`this proof)`

r -> u (by axiom 3)

`u (by modus ponens and the two preceding formula in this`

`proof)`

So the theory T proves the formula u.

`Now, suppose someone ask me for a proof of p, in the theory T. I will`

`just write the following (rather short) sequence of formula:`

p (by axiom 1).

`To proves p in one line, consisting simply in remembering one axiom.`

`That's what I meant by "provable in one line".`

Bruno Marchal wrote:Bruno Marchal wrote:Bruno Marchal wrote:Bruno Marchal wrote:Brent Meeker-2 wrote:So they don't add anything to platonia because they merely assert theexistence of existence, which leaves platonia as describedbyconsistent theories. I think the paradox is a linguistic paradox and it poses really no problem. Ultimately all descriptions refer to an existing object, but some are too broad or "explosive" or vague to be of any (formal) use.I may describe a system that is equal to standardarithmeticsbut also has 1=2 as an axiom. This makes it useless practically (or so I guess...) but itmay still be interpreted in a way that it makes sense. 1=2maymean thatthere is 1 object that is 2 two objects, so it simplyassertsthe existenceof the one number "two". 3=7 may mean that there are 3objectsthat are 7 objects which might be interpreted as aserting the existence of (for example) 7*1, 7*2 and 7*3.The problem is not that there is no possible true interpretation of 1=2; the problem is that in standard logic a falsity allows you to prove anything.Yes, so we can prove anything. This simply begs the question what the anything is. All sentences we derive from the inconsistency would mean the same (even though we don't know what exactly it is). We could just write "1=1" instead and we would have expressed the same, but in a way that is easier to make sense of. This is not problematic, it only makes the proofs in the inconsisten systemworthless (at least in a formal context were we assumeclassicallogic).And it would make Platonia worthless. The "real", genuine, Platonia is already close to be worthless due to the consistency of inconsistency for machine. This already put quite a mess in Platonia. By allowing complete contradiction, you make it a trivial object.Why? When we contradict ourselves we may simply interpret this as aexpression of the trivial truth of existence. This doesn'tchangePlantonia at all, because it exists either way.The whole point of Gödel's theorem is that M proves 0=1 is different from M proves provable('0=1'). The first implies the second, but thesecond does not implies the first. The difference between G andG*comes from this fact.If we know that something can be proven, how is it different from taking it to be proven?By incompleteness "provable(false) -> false" is not provable in the system.OK. But still "provable(false)->false" is true if we assume consistency, right? So above you meant implying as in "being a provable consequence of"?Not really. By A -> B, I mean ~A v B. Or ~(A & ~B). being a provable consequence would better be captured by B(A -> B), with "B" some provability predicate.Does "A -> B" mean B follows from A?

`It might depend what you mean by "follows from". usually, in classical`

`logic or in classical mathematics "A -> B", also written "If A then`

`B", means only that A is false or that B is true.`

`You might have seen the semantic of "A -> B". It is false only in the`

`"worlds" where A is true and B false:`

A B 1 1 in this case (A -> B) is true 1 0 in this case (A -> B) is false 0 1 in this case (A -> B) is true 0 0 in this case (A -> B) is true

`In classical logic, the false implies everything. That's why it is a`

`catastrophe if your theory proves false, because it will prove any`

`proposition.`

How is that equal to "not-A or B?"

`not A or B has the same semantic than A -> B. I let you verify. The`

`"or" is the inclusive or. For example the unique proposition "((1+1=2)`

`or (2+2 = 4))" is true.`

See? not A or B is really ((not A) or B) A B 1 1 in this case (not A v B) is true 1 0 in this case (not A v B) is false 0 1 in this case (not A v B) is true 0 0 in this case (not A v B) is true

So from provable('0=1') it does not follow 0=1, even if we assume consistency and don't mean a provable consequence?

`"provable(f) -> f" is a true formula about a consistent theory. But`

`Gödel's incompleteness makes such a formula, although true, not`

`provable by the theory itself (in case the theory is as rich to be`

`able to prove the elementary addition and multiplication laws).`

How can something be provable in a consistent system and what isproven doesnot follow?

`If the theory proves p, it will automatically prove Bp -> p. Indeed`

`for any q, it will prove q -> p. This comes from the fact that the`

`formula p -> (q -> p) is a tautology of classical propositional logic.`

`But for Löbian theories (like all the classical extension of PA) the`

`reverse is astonishingly true also, by a theoreme due to Löb, a Deutch`

`logician in 1955, if PA proves Bp -> p then PA proves p. In particular`

`PA cannot proves Bf -> f , because by Löb it would prove f.`

`A machine/theory is sound if Bp -> p is true about it. This is far`

`more demanding than being just consistent. Many consistent machines`

`can be unsound, and 'believes' false arithmetical proposition. Those`

`are satisfied by non standard models of those arithmetical theories.`

Bruno Marchal wrote:Bruno Marchal wrote:Bruno Marchal wrote:And why is inconsistency allowed for machine, but disallowed for other objects?Because if a machine proves "0=1", she will be in trouble, but if God or Platonia proves "0=1", then we are *all* in trouble.I thought we already established that 0=1 can have a clear meaning (equivalent to statements of the form 0*A+B=1*C+D in standard arithmetics), and so it poses no problem.? I have no clue what you are saying here. If "0 = 1" means "I love chocolate", then of course "0=1" might be true.But 0=1 is not plausibly interpreted as "I love chocolate" becausethelatter is not (directly anyway) a statement about numbers. 0=1 may be astatement about the two numbers 0 and 1 that is just notformulated instandard arithmetic. This does not imply that it is generally false (not anymore then peano arithmetics show there is no meaning in 0=s(n)).How could I have guessed that?Well, if someone says that" X+3=1" makes sense (and you didn't knowaboutnegative integers) you would guess he would mean a statement aboutnumbers(thereby extending the sense of numbers). Similarily you can guessthat 0=1is statement about numbers.

`Ah? All right. Just that logician makes everything explicit. There is`

`no guess needed, except in the process of finding a proof, not in`

`verifying that a sequence of formula is a proof. In particular formal`

`proof have to be automatically checkable. It can be proved that they`

`are so in the first order axiomatizable theories.`

Bruno Marchal wrote:Bruno Marchal wrote:Again, we use the standard meaning.Okay, but then 0=1 has no standard meaning in arithmetics.? But it has a standard meaning. It is just plainly false. Themeaningis "false".Well, of course, I expressed this badly. So, the statement '0=1' isfalse instandard arithmetic. But what does standard arithmetic say aboutwhat beingwrong means?

`In arithmetic, "p is wrong" means that it is not the case that p, or`

`that it is not the case that the usual structure (N, +, *) satisfies p.`

Just saying something is wrong does not really give this a meaning.

`It gives its classical meaning. We accept the classical propositional`

`calculus, including (A v ~A). All proposition in arithmetic are true`

`or false. A machine stops or does not stops when running on some`

`input, for example.`

If I know something is right, I have to know right in what way(intuitively,I might not be able to convey it), otherwise I don't really know itto beright. If I say "dfgxS" is right and I don't know what this means Idon'tknow whether it is right (other than in a trivial manner like I arguedbefore). If I say "1+1=2" is right I can imagine two objects comingtogetherand being counted. "Ahhh, in this way it is right".Similarily I have to understand wrong in what way? How do Iunderstand "1=0"is wrong beyond it just being a label?

`Well, a lot can be said here, but it might be very long, and I suggest`

`you to read some book in logic. Now, to help you shortly, to say that`

`1 = 0 is wrong should be intuitively obvious. The number 1 is not`

`equal to the number 0. 1 is the successor of zero, and no natural`

`number is equal to its successor. This is taught in high school,`

`mainly by the use of many examples. To eat 1 apple is not the same as`

`eating 0 apple. 1 $ is not the same as 0 $, .... up to the more`

`abstract statement that 0 is not equal to 1. See below for a`

`formalization of this.`

Bruno Marchal wrote:But it might still be usefully interpreted as "Try again (to make a true statement in arithmetics)"That would be a higher level heuristic. If you allow "0 = 1" to mean this, then we are no more sure what we are talking about,So what does "'0=1' is false" mean? If something is falseintuitively itmeans it is not valid in the context of a system.

`Which system? The understanding of the intuitive notion comes before`

`we build a system. In the case of capturing the (admittedly mysterious`

`intuition of numbers) we ask any system to recover the most intuitive`

`propositions on which we are agreeing. The intuition comes from living`

`among a great number of examples. To say that "0 = 1" is false means`

`that we have the intuition that one thing is not the same as zero`

`thing, for most of the usual thing we can distinguish. The fact that 0`

`is different of 1 should not be dependent on any system. if a system`

`says that 1 = 0, we should just think that the system is talking about`

`something else.`

`If not I recall that you have borrowed to me 0$ today, so that you`

`have to give me back 1,004 $ tomorrow. The 0,04 is for the interest.`

`The same is true for 2 = 0. This is just wrong, even if many algebraic`

`system satisfies 1 + 1 = 0, because that is very useful in boolean or`

`electric circuits, for example, but then 0 and 1 means something else.`

`"2 = 0" is wrong about the natural numbers because we have the`

`intuition that 2 things are different from 0 things.`

OK, but so what? This doesn't seem to be a problem? Do I have to care whether its valid?Can we really be sure what we are talking about if we are talkingaboutsomething being wrong?

`Well, if you tell me that Obama is the king of Belgium, I will have`

`some doubt about the truth of that sentence.`

`Now in science, we are NEVER sure. I might wake up and remember living`

`in a world where Obama is indeed the king of Belgium.`

Bruno Marchal wrote:or as an alternative expression of a statement inarithmetics (like treating it as an expression where some symbolsareomitted) or as expressing that all numbers are equal when we talk about an object where quantity does not matter (eg one of nothing is still nothing / 0=0*1).Yes, we are more simple minded than that. 0 = 1 is really 0 = s(0), not something else like 0 = 0*s(0).I think if we take the successor of "zero" to be "one of zero", thisis justas simple or simpler.

`? (simpler? I don't even understand what you mean! Ah you explain`

`below)`

This already makes sense if we don't really understand numbers andsometimesconflate them (eg we treat everything above 6 as equal because it is "many").

`You can't send a man on the moon with such a theory, and you can't`

`interview machine with such a theory. I can accept such a theory as an`

`example of theory, but, sorry, we need more rich theory to progress in`

`the study of machine's theology (the local goal here).`

We take 0 to be the "implicit factor" in every number so it is truethat3=3*0 and not only 3=3*1 (which implicitly means 3*0=3*1*0).

`You just illustrate that we can make any sentence true by changing the`

`theory. But the goal is the contrary: we want that our sentence`

`reflects statements about simple structure that we can define, and`

`that our axioms are understood by a majority. Concerning the natural`

`numbers (and not tension in circuit) it is better to have 2 different`

`from 0, and the same for 3. You force me to give the axioms below.`

`Congratulation :)`

One is the succesor of zero has a clear meaning, but it zero is thesuccessor of zero can have clear meaning, too. 0 represents"something (notnecessarily of quanitiy one) " in this case.Sure, we get a trivial structure if we are just concerned about whatis trueand false in this system,

`Which is the case in classical mathematics (on which quantum`

`mechanics, general relativity, computer science, etc. are based).`

but it may express something

`Anything might express something. but if we don't succeed in being`

`clear that our simplest expression expresses ONE thing, or the least`

`number possible of things, we cannot learn to discover finer nuances`

`in the sequence.`

by treating zero asplaceholder (if we don't reduce the equation to 0=0 but expand ituntilanother equality emerges, that is, until we get a truth that is not as trivial as 0=0, but still symmetric like 1=1) s(0)=0 1=0 1=s(0)1=1 "Ah, here a symmetry emerges, so this is an interestingstatement abouta trivial, yet easy to comprehend truth" ). This structure yieldsall truestatements in the same formulation that normal arithmetic does(among manymore other formulations of true statements in standard arithmetic).

You just do another theory about something else.

Certainly it's quite vague, but we could even do normal arithmeticand treatall statements not true in standard arithmetic as saying 0=0 (which isinterpreted as "falsehood" or triviality), so it's not necessarilyuseless.

`Sure. But that is not relevant for the points we were discussing,`

`although I am getting lost here.`

Actually if we don't get lost with arbitrary transformations it isno worsethan standard arithmetics.

`But only a good understanding of standard theory can help and`

`encourage the study of others, less standard theory. But in applied`

`math, we have to use the theory which are the most promising with`

`respect to the goal.`

Bruno Marchal wrote:Bruno Marchal wrote:If some my student defend ideas like 0 = 1, I give them a 0/10This is valid in mathematics, because there we agree to assumecertainaxioms and not doing this is a communication error. I don't think it is valid when doing philosophy (and interpreting what statements correspond to reality is philosopy).Philosphy, for me, is a purely private affair. I don't do philosophy,I think this is impossible.

I meant, I don't do philosophy publicly.

As soon as we state some "truth" we are doing philosophy.

`If we state that something is true, we do (bad) philosophy. Note`

`that I have never said that some statement is true. Only that some`

`statement follows from some statements. I might use those concept for`

`illustrating some point, but I have never, and will never say that`

`some statement are true.`

The concept of truth is very important though. (But that's different).

Mathematics has no meaning without truth.

`That's true, when we *assume* some kind of platonism. Many philosopher`

`of mathematics are criticizing the idea that mathematics has no`

`meaning without truth, and I could defend the idea that a big part of`

`math does not need that concept, even implicitely. I need the truth`

`(by assumption) that a machine stops or doesn't stop.`

`There is a constructive part of math which does not need the notion of`

`{0, 1} classical truth, but they will use more subtle representation`

`of truth (like subject classifier in category theory, but that's`

`demanding in abstract algebra).`

Bruno Marchal wrote:I think you don't see my point. Sure, there are statements that don't make sense or that are false in a specific system (or more informal: a specific context). That doesn't mean that these statements have no corresponding truth.But all proposition have a corresponding truth, if we allow the context to vary. The idea is that we fix the context, and then make the reasoning.OK but then we have truths in the context of the fixed of context,no more,no less.

`Yes. That's the point. We are in the context of saying yes to a`

`digitalist doctor.`

Bruno Marchal wrote:Your idea that it is somehow problematic if God proves 0=1 assumes that "0=1" has a definite meaning that is wrong.yes. The usual standard meaning. "0 = 1" is a generic proposition to give an example of a clear falsehood.But 0=1 is unclear, because we only know that it is false, notexactly whatthis means. So a clear falsehood exists only in the sense that it is clear which statements are false, not that the meaning is clear.

`I would say that with respect of the natural numbers, assuming you do`

`remember a bit what is taught in school, "0 = 1" has a clear meaning/`

`The meaning is that the natural number 0 is equal to the natural`

`number 1. I would say that this is rather clear, and rather obviously`

`wrong. About other type of numbers, or if we talk on something else,`

`it will have a clear or unclear meaning, depending on what you are`

`supposed to talk about.`

Bruno Marchal wrote:Even if we say "God proves 0=1 in standard arithmetic", we just express standard arithmetic means something else as what we commonly understand as it.That was not my use of it. I was just saying that if God proves0=s(0), we are all in trouble. That would be a catastrophe biggerthanthe big crunch. Nothing would make sense at all.See, at this point you do philosophy. You interpret something falseas "notmaking sense at all". This is simply a philosophical belief (and notone Iwould endorse).

`If God proves (by the usual means) that 0=1, it means that God is`

`inconsistent, from which provably nothing would makes sense. Oviously,`

`if God proves that 0 = 1, that can make sense only if we use "0`

`=1" (or proof) in some other sense that usual.`

I think everything does make sense, including all falsehoods.

`But if "0 = 1" is provable, then all propositions are provable. Or,`

`you are working in a private theory, and not in the public theory PA`

`(say) which capture an intuition we have about the natural numbers.`

False is relative lack of clarity or usefulness.

`I think you are confusing classical logic, with the billion of other`

`non classical logics. You might develop a logic, like the relevent`

`logic in which the notion of truth (and falsity) corresponds to what`

`you say here. But keep in mind this: classical logic is the clearest`

`of all logic, so that when you want to describe a non classical logic`

`(usually more complex and subtle) you will have to use classical logic`

`to describe it. All books on fuzzy logics have theorems proved in`

`classical logic. Now, as mathematical logic illustrates, despite the`

`simplicity of its notion of truth, classical logic is already a very`

`complex subject. And classical logic allows our ignorance to be`

`manifest. It is the logic of the theologian, not necessarily of the`

`engineers, but then they can collaborate.`

But I make it clear that it is a phliosophical standpoint (at least now I did ;) ).

`Not really. You were just suggesting some non classical logic. They`

`have many use in AI, engineering, etc. But they are build on the top`

`of classical logic.`

Bruno Marchal wrote:I don't think there is such a thing as absolutely wrong statement.If by absolutely, you mean wrong in all theories, I agree with you, but the point is a bit trivial.Indeed, in some way it is. But then existence of numbers seemstrivial, yetmany people have problems with it.

`No. Only philosopher, who believes that the presence of term like`

`consciousness, mind, reality, dreams, etc. means that we are doing`

`philosophy. It is a bit like I am saying "E = mc^2" (thinking about`

`atomic bomb) and that philosopher replies "you cannot really say that`

`energy is the mass times the square of the speed of light", for`

`philosophical reason. He might be right, in philosophy, but might be`

`obstructive obstructive in "science-and-technic".`

`Of course not so many scientists understand well that science is not a`

`question of domain (like matter = science, mind = philosophy), but of`

`attitude and methodology.`

`The existence of number used in my work is the "trivial" notion of`

`existence, where the triviality is guarantied by our (certainly`

`mysterious) intution of the natural numbers. You just need to be able`

`to solve the following puzzle: -find the simplest next terms in the`

`sequence:`

I, II, III, ., ? ., ? ...

`By simple I mean, please, the less "cutting the air" next terms. Of`

`course there are realities where`

`"IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII`

`" might be the successor of III, but we might suspect a "cutting the`

`air" notion of simplicity.`

`I manage to put the non trivial part in the theological jump you could`

`make by saying "yes to the digitalist doctor".`

The notion of triviality may be not so trivial.

It is the less trivial notion. You are right.

`But that is why it is a key to see we agree on elementary "trivial"`

`principle, like "if A is true, and if B is true, then A & B is true",`

`at least when you talking about numbers and their relations.`

`We have to start from common sense on simple things for realizing that`

`we loose control when adding a simple thing (addition for example)`

`with a simple thing (multiplication).`

That already escapes all arithmetical theories, all machines.

Bruno Marchal wrote:If by absloute, you mean wrong in all the models or intepretations of a theory about natural nulmbers, then"0=1" is indeed wrong in all interpretations of arithmeticaltheories.But what are "arithmetical theories"?

`They are set of axioms written in first order calculus predicate`

`language, with a precise formal language (&, v, ~, ), the quantifiers`

`"for-all" (A) and it-exists" (E), and the variable x, y, z, ...`

`They contain the first order predicate calculus with equality, the`

`classical tautologies, the modus ponens rule, and the first order`

`logic rules and axioms, ---all that is knwon as "classical logic", and`

`this together with the arithmetical symbols "0, s, +, *".`

Arithmetical theories are then given by the arithmetical axioms:

`Ax ~(0 = s(x)) (For all number x the successor of x is different from`

`zero). With`

`AxAy ~(x = y) -> ~(s(x) = s(y)) (different numbers have different`

`successors)`

and with different sort of axioms, containing usually the addition laws: Ax x + 0 = x (0 adds nothing) AxAy x + s(y) = s(x + y) ( meaning x + (y +1) = (x + y) +1) and the multiplication axioms Ax x *0 = 0 AxAy x*s(y) = x*y + x

`There is theory Q which has the predecessor axiom, a theory R, which`

`has some other axioms, and PA which has in addition the infinity of`

`formula of the shape`

`(F(0) & Ax(F(x) -> F(s(x))) -> AxF(x), with F(x) being a formula in`

`the arithmetical language (with "0, s, +, *), and the logical symbols`

`as said above.`

`They are many of them, but for the sound one, above some threshold`

`(mainly given by the induction axioms) they obey to the arithmetical`

`hypostases, and they can formulate the WR problem.`

Can this even be defined? Maybe there is an arithmetical theory where 0=1 is true.

Yes indeed, there is many one. Take anyone above, and adds the axiom "0 = 1".

`Well, then you have to weaken the logical rules in some ways (among`

`many) to keep the theory interesting. With most logic, classical,`

`intuitionist, even quantum logic having that "0=1" will trivialize the`

`theory (making all statement true). But in the relevant logic "0=1"`

`can be less damageable, but not yet so interesting. I suspect the`

`fifth hypostase to be an arithmetical relevant logic, and this could`

`mean that "0 = 1" can play a role. In fact, in G it does already play`

`a role to in the consistency of inconsistency. not provable false`

`implies not provable (not provable false), and take "0 = 1" as meaning`

`false.`

If you are interested, you might have to study some logic books.

`Those theories are the *object* of study. They are machine theorem`

`provers with infinite ressource (that "Platonia"). Logicians study`

`both the theories/machines and their web of interpretations/semantics.`

`It is a branch of math.`

Bruno Marchal wrote:Allfalsehood is depended on assuming certain axioms - while truth isnot.That makes truth even more absolute.Well, that's good in my mind. Truth seems to be the most absolutething forme.

OK. (I mean we might agree on this).

Bruno Marchal wrote:I think it is an error to say "if God or Platonia proves "0=1", then we are *all* in trouble." because we can't say what it would mean if God proves 0=1 according to the axioms we use. Or it means simply that God states things that are wrong in certain systems, which also poses no problem.Well, if God actually comes by, and says "0 = 1", I will conclude something like "oh! God has some sense of humour", or I will think that's not God, or I will thinks "I must be dreaming", etc.I meant actually proving.

Then pigs have wings. And here is a white rabbit, and two others there.

Of course we don't know what it would mean if God would prove 0=1 according to our axioms, but this is my point.

`It would mean, by definition, that God uses an inconsistent`

`arithmetical theory. Which one precisely?`

Bruno Marchal wrote:I would not insist on this so much if I would not suspect that consideringthe possibility of something being an "ultimate falsehood" or"totallywrong" leads to disregarding some statements instead of seeing their truth. We don't have to avoid "wrong" statements. They simply are not as proliferative as (more) true statements.I disagree. Most statements in most (non arithmetical) theories are wrong.It's hard to tell, I think. In most theories there is not even anabsolutelyclear distinction between right and wrong.

`For all "enough rich" or Löbian theories, the border between right and`

`wrong countains the fractal shapes of the border between the provable`

`and the refutable. Universal numbers are confronted with the whole`

`richness of the geometry separating right and wrong. It is like the`

`border of the mandelbrot set.`

Physical theories for example are (as far as we now) never completely right, so are they wrong?

Very difficult question. (without or with comp).

Bruno Marchal wrote:Bruno Marchal wrote:My suggestion is that every statement has such an interpretation. Circles with edges makes sense if we allow hyperreal numbers as numbers of edges andlenght of edges, triangles with four sides may mean such ageometricobject:http://commons.wikimedia.org/wiki/File:Triangle-square-area-dev.pngand that God is omnipotent may mean anything.Logic has been invented for avoiding interpretations as much as possible, and then for studying mathematically what can beinterpretations, and the relations (Galois connection) betweenformaldeduction and relations on interpretations. We force the"propositions" which mean anything to be eliminated, for helpingtheprogress toward genuine truth and meaning.We can say that first order logic does succeed in theinterpretationelimination, thanks to a theorem of completeness (notincompleteness)by Gödel. A formula is a theorem IF and ONLY IF the formula is true in all interpretations.Again, this is true, but it depends on certain axioms, which can be interpreted to be not right in all contexts.I disagree. The completeness theorem of Gödel does not depend on anyaxioms, just on the definition of what is a first order logicaltheoryand an interpretation (model). Note that such a theorem is no more true for higher order logics, which makes them almost as vague as mathematics, for some logicians.Maybe we don't need explicit axioms, but we need implicit assumptions.

`Exactly. Always, even when we talk about machine. But to study this`

`for machine necessitates to handle first the simplest case of ideally`

`correct machines, and the surprise is that it leads to a transfinite`

`ladder of difficulties. That little "universal (Turing) machine", or a`

`degree four Diophantine equation already put quite a mess in Platonia,`

`and the sound machine can only acknowledge the difficulties.`

If we define a first order logical theory and have aninterpretation, tovalidly prove anything we must at least assume that these definitions/interpretation are meaningful.

`Sure, but we have a tons of models, so we find them meaningful. Just`

`that we discover that they are rich of unexpected structures. It is`

`because we make the rule clear and simple that we can, by using the`

`"mathematical logical 'Hubble' to discover the complexity of the`

`subject.`

Otherwise we can just reject them by not finding them meaningful andthusreject any proof derived from it.

`That happens, and happened many times. Both Curry and Church, and`

`Frege, have developed theories which have fallen down literally, by`

`being shown to be inconsistent. New theories emerges from that. That`

`happens all the times. Sometimes a theory survives by its`

`interpretation evolving, and vice versa.`

`There is a 'Galois connection' between theories and their`

`interpretation, like between equation and surface. That is: the less a`

`theory has axioms, the more it has interpretations.`

`When we have to take into account the internal interpretations build`

`by the objects of the theories themselves, it is even far more`

`complex, but both comp and the quantum gives non trivial hints.`

Bruno http://iridia.ulb.ac.be/~marchal/ -- You received this message because you are subscribed to the Google Groups "Everything List" group. To post to this group, send email to everything-list@googlegroups.com. To unsubscribe from this group, send email to everything-list+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/everything-list?hl=en.