Logic 11-15 - Logic Presentation Review helpful terminology...

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Logic Presentation Logic Presentation November 15, 2007 November 15, 2007
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Review: helpful terminology Review: helpful terminology A statement of the form If P then Q is called a conditional . P is called the antecedent , and Q is called the consequent . Conditional If Fr. Dease is in St. Paul , then Fr. Dease is in Minnesota . Example: Antecedent Consequent
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Review: Modus Ponens Review: Modus Ponens 1. If P , then Q . 2. P . 3. Therefore, Q . Example : 1. If music be the food of love , then you should play on . 2. Music is the food of love . 3. Hence, you should play on .
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Review: Modus Ponens Review: Modus Ponens Modus Ponens If P , then Q . P . Therefore, Q . Not Modus Ponens If P , then Q . Q . Therefore, P .
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Review: Modus Tollens Review: Modus Tollens 1. If P , then Q . 2. Not Q . 3. Therefore, not P . Example : 1. If the universe were devoid of dark matter , then galaxies would fly apart . 2. It is not the case that galaxies fly apart . 3. Thus, it is not the case that the universe is devoid of dark matter .
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Review: Modus Tollens Review: Modus Tollens Not Modus Tollens If P , then Q . Not P . Therefore, not Q . Modus Tollens If P , then Q . Not Q . Therefore, not P .
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Hypothetical Syllogism Hypothetical Syllogism 1. If P , then Q . 2. If Q , then R . 3. Therefore, if P , then R .
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Hypothetical Syllogism: Hypothetical Syllogism: If P, then Q. If Q, then R. Therefore, if P, then R. If P, then Q. If Q, then R. Therefore, if P, then R. Example III 1. If all the world’s a stage , then all the men and women are merely players . 2. If all the men and women are merely players , then they all have their exits and their entrances . 3. Thus, if all the world’s a stage , then all the men and women have their exists and their entrances . Example I 1. If the sun is a variable star , then its energy will drop drastically at some point . 2. If the sun’s energy drops drastically at some point , then the earth will become a huge iceball . 3. Hence, if the sun is a variable star , then the earth will become a huge iceball . Example II 1. If I ever lose my mouth , then I’ll lose all my teeth, north and south . 2. If I lose all my teeth, north and south , then I won’t have to talk . 3. Thus, if I ever lose my mouth , then I won’t have to talk .
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Disjunctive Syllogism Disjunctive Syllogism 1. P or Q . 2. Not P . 3. Therefore, Q .
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Disjunctive Syllogism: P or Q. Not P. Therefore, Q Disjunctive Syllogism: P or Q. Not P. Therefore, Q Example III 1. Either you’re Mr. Rochester or I’m dreaming right now . 2. It’s not the case that you’re Mr. Rochester . 3. Therefore, I’m dreaming right now . Example I 1. Last Sunday, either the Vikings won or the Packers won . 2.
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This note was uploaded on 04/07/2008 for the course PHIL 115 taught by Professor Stoltz during the Fall '07 term at St. Thomas.

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Logic 11-15 - Logic Presentation Review helpful terminology...

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