## Sunday, September 25, 2011

### Logical Fallacy of the Week, Week 9: Prepositional Fallacies

We now will explore those fallacies called;

Prepositional Fallacies

In mathematical logic, a propositional calculus or logic (also called sentential calculus or sentential logic) is a formal system in which formulas of a formal language may be interpreted as representing propositions. A system of inference rules and axioms allows certain formulas to be derived, called theorems; which may be interpreted as true propositions. The series of formulas which is constructed within such a system is called a derivation and the last formula of the series is a theorem, whose derivation may be interpreted as a proof of the truth of the proposition represented by the theorem.  Truth-functional propositional logic is a propositional logic whose interpretation limits the truth values of its propositions to two, usually true and false. Truth-functional propositional logic and systems isomorphic to it are considered to be zeroth-order logic.

This is another of those fallacies that is unendingly complicated, so it probably will have no value in the real world. This appears to be an attempt to quantify fallacies mathematically. At least that is what I get out of this. Most of us will have no use for this piece, but it is next in line and I have decided to list the fallacies under this subcategory in order to lend understanding to the whole category. Please follow the links for the explainations, which are much easier to understand. RK

Affirming a disjunct: concluded that one logical disjunction must be false because the other disjunct is true; A or B; A; therefore not B.

Affirming the consequent: the antecedent in an indicative conditional is claimed to be true because the consequent is true; if A, then B; B, therefore A.

Denying the antecedent: the consequent in an indicative conditional is claimed to be false because the antecedent is false; if A, then B; not A, therefore not B.