PHILOS 31 Study Guide - Midterm Guide: Disjunctive Syllogism, Modus Ponens, Modus Tollens
Document Summary
If you still have not completed your proof and one of your lines is the negation of a conditional [ ~( )], show the conditional itself [ ( )] in order to generate a contradiction. If one of your lines is the negation of a disjunction [~( (cid:1664) )], see if you can use add with another line to get the disjunction itself [( (cid:1664) )], in order to generate a contradiction. (b). Look for disjunctions that you have not yet broken down ( (cid:1664) ), and try to show the negation of one of the (a). You can also use cdj to show disjunctions (although using indirect derivation with dm works just as well). For ^ (and), the statement is true only if both are true. For v (or), one or more parts of the statement must be true for the statement to be true. Only false if the antecedent is true and the consequent false.
