Wednesday, June 1, 2016

The Illogical nature of formal logic or the emperor has no clothes

Formal logic is based on modus ponens (A, if A then B, therefore B) in the sense that modus ponens is often considered the paradigmatic valid logical form.  However modus ponens begs the question, not just sometimes but always because of its form.  The whole idea of validity is to make a neat transition from A (the reason being offered) to B (the thing supported, i.e. the conclusion) by way of introducing an intervening premise, i.e. if A then B. However, you cannot support the move from A to B just by repeating it!  That is begging the question.  A typical strategy in argument analysis is to take a real world argument where someone offers A in support of B and then hypothesize an intervening non-stated premise to make it valid:  if A then B.  It is true that we give reasons in support of conclusions.  However, if others accept them it is not because of artificial question-begging intervening premises previously accepted, but because they believe A is sufficient reason for B. Modus Ponens is a sham, and it is the paradigm of argumentation in formal logic. So formal logic is a sham.  (Logicians might try to refute me by claiming that I have intervening premises.  I deny the intervening premises exist or are part or or needed for my own argument.)  

Of course one can have a notion of "valid" which simply means an argument in which the conclusion follows from the premises including all of the relevant evidence.  If B follows from A then the argument is valid.  No need to introduce "if A then B" to prove this or back it up!  It doesn't help. It is window-dressing. 

It may no longer make sense to speak of arguments that are valid and not sound.  How could A support the truth of B if A is not itself well supported or obviously true? 

Formal logic is useful in mathematics and computer science. However this has nothing to do with preserving truth.  The application of formal logic to issues in ethics, aesthetics and even science is pretty much nonsense.  

I do not claim that my argument against modus ponens is original. I seem to recall seeing something similar many years ago but cannot remember the source. 

1 comment:

Dan T said...
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