Section8.8 - Section8.8 Review P1 If lightning strikes then it will thunder(statement P2 Lightning strikes L C It will thunder T Substitution Instances

Section8.8 Review P1: If lightning strikes then it will thunder (statement) L  T (statement) P2: Lightning strikes L C: It will thunder T  Substitution Instances p(statement form) q therefore: r argument form specific argument form: p  q(specific statement form) p therefore: q argument forms where there are substitution instances, and statement forms where there are substitution instances Statement Forms: 1. The US invaded Iraq in 2003 I p 2. Either the US invaded Iraq or the US did not invade Iraq I v ~I p v ~p • both true statements Statement 1: empirical truth Statement 2: logical truth • True in virtue of their form • Any statement with this form has to be true no matter what is plugged in for p P ~p P v ~p T F T F T T Statement form of a logical truth is called a tautology • Tautology- a statement form all of whose substitution instances are true • Contradiction o Statement form all of whose substitution instances are false/logical falsehoods p • ~p P ~p P•~p