On May 26, 4:49 pm, Nam Nguyen <namducngu...@shaw.ca> wrote: > On 26/05/2013 3:52 AM, Zuhair wrote: > > > > > > > > > > > On May 26, 11:03 am, Nam Nguyen <namducngu...@shaw.ca> wrote: > >> On 26/05/2013 12:52 AM, Zuhair wrote: > > >>> Frege wanted to reduce mathematics to Logic by extending predicates by > >>> objects in a general manner (i.e. every predicate has an object > >>> extending it). > > >> [...] > > >>> Now the above process will recursively form typed formulas, and typed > >>> predicates. > > >> Note your "process" and "recursively". > > >>> As if we are playing MUSIC with formulas. > > >>> Now we stipulate the extensional formation rule: > > >>> If Pi is a typed predicate symbol then ePi is a term. > > >>> The idea behind extensions is to code formulas into objects and thus > >>> reduce the predicate hierarchy into an almost dichotomous one, that of > >>> objects and predicates holding of objects, thus enabling Rule 6. > > >>> What makes matters enjoying is that the above is a purely logically > >>> motivated theory, I don't see any clear mathematical concepts involved > >>> here, we are simply forming formulas in a stepwise manner and even the > >>> extensional motivation is to ease handling of those formulas. > >>> A purely logical talk. > > >> Not so. "Recursive process" is a non-logical concept. > > >> Certainly far from being "a purely logical talk". > > > Recursion is applied in first order logic formation of formulas, > > Such application isn't purely logical. Finiteness might be a purely > logical concept but recursion isn't: it requires a _non-logical_ > concept (that of the natural numbers). > > > and all agrees that first order logic is about logic, > > That doesn't mean much and is an obscured way to differentiate between > what is of "purely logical" to what isn't. >
Yes I do agree that this way is not a principled way of demarcating logic. I generally tend to think that logic is necessary for analytic reasoning, i.e. a group of rules that make possible to have an analytic reasoning. Analytic reasoning refers to inferences made with the least possible respect to content of statements in which they are carried, thereby rendering them empirically free. However this is too deep. Here what I was speaking about do not fall into that kind of demarcation, so it is vague as you said. I start with something that is fairly acceptable as being "LOGIC", I accept first order logic (including recursive machinery forming it) as logic, and then I expand it by concepts that are very similar to the kind of concepts that made it, for example here in the above system you only see rules of formation of formulas derived by concepts of constants, variables, quantifying, definition, logical connectivity and equivalents, restriction of predicates. All those are definitely logical concepts, however what is added is 'extension' which is motivated here by reduction of the object/predicate/predicate hierarchy, which is a purely logical motivation, and also extensions by the axiom stated would only be a copy of logic with identity, so they are so innocuous as to be considered non logical. That's why I'm content with that sort of definitional extensional second order logic as being LOGIC. I can't say the same of Z, or ZF, or the alike since axioms of those do utilize ideas about structures present in mathematics, so they are mathematically motivated no doubt. NF seems to be logically motivated but it use a lot of mathematics to reach that, also acyclic comprehension uses graphs which is a mathematical concept. But here the system is very very close to logic that I virtually cannot say it is non logical. Seeing that second order arithmetic is interpretable in it is a nice result, it does impart some flavor of logicism to traditional mathematics, and possibly motivates logicism for whole of mathematics. Mathematics might after all be just a kind of Symbolic Logic as Russell said.
> > similarly here > > although recursion is used yet still we are speaking about logic, > > formation of formulas in the above manner is purely logically > > motivated. > > "Purely logically motivated" isn't the same as "purely logical". >
A part from recursion, where is the mathematical concept that you isolate with this system? > -- > ---------------------------------------------------- > There is no remainder in the mathematics of infinity. > > NYOGEN SENZAKI > ----------------------------------------------------