PHI 1101 Lecture Notes - Lecture 15: Modus Tollens, Modus Ponens, Hypothetical Syllogism

• School: University of Ottawa
• Department: Philosophy
• Course: PHI 1101
• Professor: Iva Apostolova

Document Summary

4 valid argument forms: modus ponens (affirming the antecedent) Eg: if it rains today, the ground will be wet. (p=> q) it rained today. (p) therefore, the ground will be wet. (q: modus tollens (denying the consequent) Eg: if putnam is guilty, he is lying now. (p => q) he is not lying now. (~q) therefore, putman is not guilty. (~p: chain argument (hypothetical syllogism) Q => r / p => r (if q, then r. if p, then r) (to make p => r, you need p =>q=>r) Eg: if taxes go up, inflation goes down. (p =>q) if inflation does down, most people are better off. (q => r) therefore, if taxes go up, most people are better off. (p =>r: disjunctive syllogism. Eg: either picasso was this century"s greatest artist or klimt was. (cid:523)pvq(cid:524) klimt wasn"t. (cid:523)~q(cid:524) Therefore, picasso was this century"s greatest artist. (cid:523)p(cid:524)