Difference in Rules of Inference, Gensler and Copi
  • hateloveschool
    3
    When I took Logic in college we used Gensler's Introduction to Logic. I really liked it, concise, clear and logicola was extremely helpful.

    Recently I picked up Copi's book Introduction to Logic and noticed that he uses different Inference Rules. Why is there such a difference? For example: Gensler does not use De Morgan's theorem while Copi does not use rules like: ⌐(A ⊃ B) ∴ A, ⌐ B.

    I understand the distinction Gensler makes between S-Rules and I-Rules as well as Copi's distinction between Elementary Valid Argument Forms and Logically Equivalent Expressions. I do not understand why they have different rules for what is called the same, propositional logic, what am I missing?
    hateloveschool Options
  • fdrake
    6.6k
    The choice of rules doesn't ultimately matter much, what matters is what theorems you can derive from them. All the classical propositional logics have the same theorems, they just start from different assumptions/rules of inference.

    This gets called "interderivability"; for two given lists of inference rules (or more generally, propositions), if you can derive all of the consequences of one from the other and vice versa the lists are interderivable.
    fdrake Options
  • hateloveschool
    3
    ↪fdrake
    Thanks, that's helpful, is their a source that gives a list of all the different kinds?
    hateloveschool Options
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