Phil 105, Week 2 Notes
Phil 105, Week 2 Notes PHIL 105 - 01
Cal State Fullerton
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This 4 page Class Notes was uploaded by Katrina Japson on Friday January 29, 2016. The Class Notes belongs to PHIL 105 - 01 at California State University - Fullerton taught by Richard Vulich in Spring 2016. Since its upload, it has received 34 views. For similar materials see Critical Thinking in PHIL-Philosophy at California State University - Fullerton.
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Date Created: 01/29/16
PHIL 105 2/2 Deductive Arguments vs. Inductive Arguments Deductive Argument – An argument where if all the premises are true, then the conclusion must necessarily be true also o If the premises are true, then the conclusion must be true. o Generate premises that logically in tale the conclusion. o Ex. All men are mortal. Socrates is a man. Therefore, Socrates is mortal. This argument is valid. This is a sound argument. o Ex. The killer used either a knife or a gun. The killer did not use a knife. Conclusion: The killer used a gun. This argument is valid too. The conclusion follows from the premises. o Sound argument – An argument that is valid AND all of the premises are in fact true. But not all valid arguments are sound. Ex. All men have 8 legs. Obama is a man. Obama has 8 legs The argument is valid because suppose all men have 8 legs. Since Obama is a man, it is valid to conclude Obama has 8 legs. HOWEVER, because one of the premises is in fact NOT true (All men have 8 legs), the argument is NOT sound. Ex. All girls have blue eyes. Beyoncé is a girl. Beyoncé has blue eyes. The argument is valid because suppose all girls have blue eyes. Since Beyoncé is a girl, it is valid to conclude she has blue eyes. HOWEVER, because one of the premises is NOT true (All girls have blue eyes), the argument is NOT sound. Ex. All humans are mammals. All mammals need water to survive. All humans need water to survive. This argument is both valid AND sound because BOTH premises are in fact true, therefore the conclusion is true. So, all sound arguments are valid but not all valid arguments are sound. Inductive Argument – An argument where if the premises are true, then the conclusion is high likely/probably true o Used in cases where predictions are made based on patterns that have been seen in the past o Ex. The sun has risen every morning for billions of years Conclusion: The sun will rise tomorrow. Even if the premises are true due to a consistent pattern, it isn’t 100% the conclusion will be true. o Ex. I have woken up everyday for the past 18 years I will wake up tomorrow. Although the premises are true because I have woken up everyday for the past 18 years, it isn’t completely true that I will wake up tomorrow. o All inductive arguments are invalid. PHIL 105 2/4 Deductive Arguments The premises prove the conclusion or establish it with certainty Syllogisms – Valid arguments containing only 2 premises o Ex. All A’s are B’s. X is an A. X is a B Valid form of deductive argument o Argument will remain valid regardless Argument by Elimination/Disjunctive Syllogism o Disjunction – an “either/or” sentences o They all take the form of A or B. o Premise 1: Either A or B. Premise 2: Not A. Conclusion: B o Ex. The killer either used a gun or a knife. Killer did NOT use a knife. Killer used a gun. Hypothetical syllogism o Conditional sentences – “if/then” sentences “If…” – antecedent, “then…” – consequence Ex. If I study, then I will pass. If I eat, then I won’t be hungry. o 3 types of hypothetical syllogism arguments 1. Modus Ponens – Affirming the antecedents Premise 1: If P, then Q. Premise 2: P. Conclusion: Q Ex. If I jump off the bridge then I will die. I jumped off the bridge. I died. Ex. If I eat dinner then I won’t be hungry. I ate dinner. I’m not hungry. 2. Modus Tollens – Denying the consequent Premise 1: If P, then Q. Premise 2: Not Q. Conclusion: Not P. Ex. If you come over, then I’ll take you to lunch. I didn’t take you to lunch. You didn’t come over. Ex. If I water the plants, then the plants will grow. The plants aren’t growing. I didn’t water the plants. 3. Chain Argument – Makes use of conditional sentences Premise 1: If A, then B. Premise 2: If B, then C. Conclusion: If A, then C. Ex. If domino A topples, then domino B will topple. If domino B topples, then domino C will topple. If domino A topples, then domino C will topple. Ex. If I don’t go to work, then I won’t get paid. If I don’t get paid, I won’t have spending money. If I don’t go to work, I won’t have spending money. Ex. If I go to bed late, then I will wake up late. If I wake up late, I will be late to my first class. IF I go to bed late, I will be late to my first class.
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