SSH 105 Lecture Notes - Lecture 5: Modus Tollens, Modus Ponens

• School: Ryerson University
• Department: Social Sciences and Humanities
• Course: SSH 105
• Professor: David Hunter

Document Summary

When we try to decide what to believe, we do so by ruling out the options. Either the maid did it or the butler did it, but the maid couldn"t have done it, so the butler did it. Disjunctions asserts that at least one of the disjunctions is true. Disjunction is inclusive if all of its disjuncts can be true at once. Either jim is on the team or bob is on the team. If a disjunction is true but one disjunct is false, you assume the other is true. Denying a disjunct where the disjunction is false will always lead to a false conclusion. Disjunction is exhaustive when it includes all the possibilities. Knowing all the options is often very difficult and could take years of study. Disjunction is exclusive when its disjuncts cannot all be true. Either jane is pregnant or she is not.