Hi John,

On 18 May 2009, at 21:00, John Mikes wrote:

> Bruno:
>
> could you tell in one sentence YOUR identification for logic?

That is a difficult question, and to be honest, I am still searching.  
As a platonist (that is: classical logician) I am OK with the idea  
that logic is the abstract (domain independent) study of the laws of  
thought, although I would add probability theory to it (like Boole).



> (I can read the dictionaries, Wiki, etc.)
> I always say :common sense, but what I am referring to is
>    -- --  M Y -- -- common sense,
> distorted - OK, interpreted - according to my genetic built, my  
> experience (sum of memories), instinctive/emotional traits and all  
> the rest ab out what we have no idea  today yet.

I can agree with this, althought the aim is too suppress as far as  
possible the distortion.


>
> I never studied 'formal' logic, because I wanted to start on my own  
> (online mostly) and ALL started using signs not even reproducible on  
> keyboards

That is why Knuth invented LATEX :)



> and not explained what they are standing for. As I guessed: the  
> 'professors' issued "notes" at the beginning of the college-courses  
> (($$s?)) and THERE the students could learn the 'vocabulary' of  
> those signs.
> You also use some of them.

I think you are pointing the finger on the real difficulty of logic  
for beginners. You are supposed not to attribute meaning on those  
signs, because what the logician is searching for is rule of reasoning  
which does not depend on the meaning. The hardness of logic is in the  
understanding of what you have to NOT understand to proceed. Logicians  
take the signs as just that: sign, without meaning. Then they will  
develop rule of transformation of those sign, in such a way that  
machine can play with them, and mathematical rule of meaning, and they  
are happy when they succeed to find nice correspondence between rule  
and meaning. It makes the subject both very concrete and abstract at  
the same time. I am used to think that logic is the most difficult  
branch of math. Somehow, computer science makes it more easy. It  
motivates the point of not trying to put meaning where none is  
supposed to be.




>
> I was looking at a dozen books as well and did not find those signes  
> explained, not in footnotes, not in appendicis, not as intro- or  
> post- chapters. They were just applied from page 1.
> So I gave up.

I can understand. It is hard to study logic alone. Yet there are good  
books, but it takes some effort to understand where you have to take  
those sign literally. I would suggest the reading of the little  
penguin book by Hodges "Logic", which is perhaps clear for an  
introduction.
Logic is laso hard to explain to the layman, because it concerns  
objects which look like formal things, and it takes time to understand  
that we study those objects without interpreting them. beginners take  
time to understand the use of saying that, for example, we will say  
that "A & B" is true when A is true and B is true. They can believe  
that they learn nothing here, but they are false because the "&" is  
formal, and the "and" is informal. After all you do learn something if  
I say that "A et B" is true when A is true and B is true. In this case  
you learn french, which are at the same level of informality, but in  
logic you attach rules and meaning to explicitly formal things on  
which you reason *about*.
To ask a logician the meaning of the signs, is a bit like asking a  
biologist the meaning of "ATTAGTTCAATCCCT" or DNA. It is like asking  
the logician what is logic, and no two logicians can agree on the  
possible answer to that question.  When student ask some question  
here, it is not rare the answer he get is just "we are not doing  
philosophy here". The object study is far more concrete than beginners  
can imagine, and that is why the notion of machine and computer  
science can help a lot for many parts of logic.

Bruno


http://iridia.ulb.ac.be/~marchal/




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