# SSH 105 Chapter Notes - Chapter 5.1: Modus Ponens, Grass Green, Modus Tollens

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## Document Summary

10:47 pm: sometimes, we can tell just from the logical form of an argument whether it is valid. In this chapter: reasoning using (cid:494)or(cid:495) and (cid:494)if, then(cid:495). Often when we try to decide what to believe or do we are faced with several options, and we reason by ruling them out one by one. Either the maid did it or the butler did it; but the maid could not have done it; so, the butler is guilty! reasoning used to set out alternatives to narrow down a specific cause. A disjunction asserts that at least one of the disjuncts is true. A disjunction is inclusive if all of its disjuncts can be true at once. Either steven is a student or a professor. If you know that a disjunction is true, and you discover that one disjunct is not true, then you can conclude that the other one must be true. This reasoning is a matter of ruling out possibilities.

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