*Originally posted by vivify*

**Logic is formed with evidence.
**

End thread.

Actually I think this is an interesting point. My view is that logic is a formal language with grammatical rules for generating sentences. For example, Classical logic has

*reductio ad absurdum* (If A implies a contradiction it is false, so not(A) is true),

*or insertion* (if A is true then (A or B) is true), and the

*double negative rule* (if not(not(A)) then A), as allowed operations, so we can deduce the

*law of divided middle* as a consequence - suppose P is any proposition:

1) Assume not (P or not(P))

2) Assume P

3) (P or not(P)) - From (2) by

*or insertion*.

4) Not P - (3) contradicts (1) and depends on (2) so the converse of (2) follows by

*reductio*.

5) P or not(P) - follows from (4) by

*or insertion* and depends only on (1).

6) not(not(P or not(P))) - (5) contradicts (1) and depends on it so the

*reductio* rule shows the initial assumption of (1) is false.

7) P or not(P), from the

*double negative* rule applied to 6.

The last step (7) would not be agreed to by intuitionistic logicians. They regard the double negative rule as flawed (not unhappy does not imply happy). So, although I'm happy to believe the result,

*it hangs on a collection of grammatical rules* and is only true if the propositions exhaust all the possibilities. Classical logic is expected to preserve truth, while intuitionistic logic preserves provability, so which you use for a particular purpose depends on the problem. Logic controls what one can consistently say about the world, it does not control the world.

What I'm getting at is that I think Fetchmyjunk is right to point out that logic is dependent on mind. In fact, he might also point out that all scientific theories are written in a language (typically US English with additional technical terms) and have rules for making deductions. You could regard a scientific theory as a program for a Universal Turing Machine, one simply gives it the theory and asks it some propositional question to some precision, where the user can specify any finite precision - for example, given these quark masses, these coupling strengths and the Standard Model of Particle Physics, what is the mass of the proton to 3 significant figures - and the machine would click, buzz, hum and churn out the answer that you could then compare with experiment. A fundamental assumption of all Science is that this process will work and that nature is

*reliably* describable in this way. Our only justification for this is that it seems to have worked quite well so far...

This is where I think the problem with Fetchmyjunk's O.P., as a critique of Science and Logic it's fine, but he seems to want to make God the provider of logic. Since I'm almost certain that deductive rules are not specified by this he seems to have a theory of natural logic. So his argument seems to be predicated on the notion that logic is built into the structure of the universe just because it can describe the universe and there's no reason to believe that - "Ceci n'est pas une pipe."