DEBATE Logic Deduction and Induction Logic an introduction

DEBATE Logic: Deduction and Induction

Logic: an introduction to key concepts ◦ Deduction: A conclusion that MUST come from the premises (or circumstances). All other logical methods (and mathematical conclusions) are based on deduction. ◦ Deductions follow this pattern: if a = b and b = c, then a = c ◦ For example: ◦ First premise: All middle school teachers are human. ◦ Second premise: I am a middle school teacher. ◦ Conclusion: I am human. Is the first premise COMPLETELY true? Is the second premise COMPLETELY true? Then the conclusion MUST be true.

Logic: an introduction to key concepts ◦ Sometimes, people base conclusions off of false premises ◦ For example: ◦ First premise: Most middle school teachers are human. ◦ Second premise: I am a middle school teacher. ◦ Conclusion: I am necessarily human. Is the first premise COMPLETELY true? Is the second premise COMPLETELY true? Then the conclusion MUST be true.

Logic: an introduction to key concepts ◦ Sometimes, the premises are valid, but the conclusion is wrong. ◦ For example: ◦ First premise: Middle school teachers are human. ◦ Second premise: I am a middle school teacher. ◦ Conclusion: I am not human. Is the first premise COMPLETELY true? Is the second premise COMPLETELY true? Then the conclusion MUST be true.

Logic: Check for understanding ◦ Sometimes, the premises are valid, but the conclusion is wrong. ◦ For example: ◦ All dolphins are mammals, all mammals have kidneys; therefore all dolphins have kidneys. Yes - Logical deduction! Is the first premise COMPLETELY true? Is the second premise COMPLETELY true? Then the conclusion MUST be true.

Logic: Check for understanding ◦ Sometimes, the premises are valid, but the conclusion is wrong. ◦ For example: ◦ Since all rhombuses are rectangles, and all rectangles have four sides, so all squares have four sides. No – false premise! Is the first premise COMPLETELY true? Is the second premise COMPLETELY true? Then the conclusion MUST be true.

Logic: Check for understanding ◦ Sometimes, the premises are valid, but the conclusion is wrong. ◦ For example: ◦ All numbers ending in 0 or 5 are divisible by 5. The number 35 ends with a 5, so it is divisible by 5. No – conclusion is not valid! Is the first premise COMPLETELY true? Is the second premise COMPLETELY true? Then the conclusion MUST be true.

Logic: Check for understanding ◦ Sometimes, the premises are valid, but the conclusion is wrong. ◦ For example: ◦ Dennis will miss work today. At work, there might be a party. Dennis will miss a party today. Yes - Logical deduction! Is the first premise COMPLETELY true? Is the second premise COMPLETELY true? Then the conclusion MUST be true.

Logic: Check for understanding ◦ Sometimes, the premises are valid, but the conclusion is wrong. ◦ For example: ◦ All birds have feathers and robins are birds, so eagles have feathers. No – conclusion is not valid! Is the first premise COMPLETELY true? Is the second premise COMPLETELY true? Then the conclusion MUST be true.

Logic: Check for understanding ◦ Sometimes, the premises are valid, but the conclusion is wrong. ◦ For example: ◦ It is dangerous to drive on icy streets. The streets are icy now so it is dangerous to drive now. Up for debate. Are the premises always true? Is the conclusion always true? Is the first premise COMPLETELY true? Is the second premise COMPLETELY true? Then the conclusion MUST be true.

Turn & Talk ◦ What premises support the conclusions: ◦ Middle school is hard ◦ Middle school students are adolescents

Logic: an introduction to key concepts Why is this important? : ◦ Induction: The reasoning of estimating -- making a really good guess -- about Almost all day-to-day logical reasoning uses this method. It’s how people decide whether observation(s) are true orderato give evidence for aon conclusion. whether they should cross theinstreet certain way. It relies observation and experience instead of logic alone. Because of this, induction is OFTEN ILLOGICAL. ◦ (Basically: If something canthink reasonably be inferred to be true, a conclusion Many people incorrectly their inductive reasoning to make a decisionabout is deductive, which can result in being wrong and open to logical attack. it must be true. ) ◦ Inductions must have one observation and one conclusion based on that observation.

Induction CFU Can you arrive at these same conclusions using deductive reasoning instead of inductive reasoning? ◦ Observation 1: Yunilza and Abdullah are always on time to school. ◦ Observation 2: Yunilza and Abdullah always leave for school by 7: 00 AM at the latest. ◦ Conclusion: Yunilza and Abdullah will always be on time to school if they leave by 7: 00 AM. Why could this conclusion be faulty?

Induction CFU Can you arrive at these same conclusions using deductive reasoning instead of inductive reasoning? ◦ The chair in the living room is red. ◦ The chair in the dining room is red. ◦ The chair in the bedroom is red. ◦ Conclusion: All chairs in the house are red. Why could this conclusion be faulty?

Induction CFU Can you arrive at these same conclusions using deductive reasoning instead of inductive reasoning? ◦ Every time you eat peanuts, your throat swells up and you can't breath. ◦ Conclusion: You are allergic to peanuts. Why could this conclusion be faulty?

Induction CFU Can you arrive at these same conclusions using deductive reasoning instead of inductive reasoning? ◦ All cats that you have observed purr. ◦ Conclusion: every cat must purr. Why could this conclusion be faulty?

Induction CFU Can you arrive at these same conclusions using deductive reasoning instead of inductive reasoning? ◦ Two-thirds of the students at this college receive financial aid. ◦ Conclusion: Two-thirds of all college students receive student aid. Why could this conclusion be faulty?

Induction CFU Can you arrive at these same conclusions using deductive reasoning instead of inductive reasoning? ◦ Bob is showing a big diamond ring to his friend Larry. ◦ Bob has told Larry that he is going to marry Joan. ◦ Conclusion: Bob has bought the diamond ring to give to Joan. Why could this conclusion be faulty?

Application: Affirmative Action (con) ◦ Premise 1: Affirmative action favors minorities along racial lines. ◦ Premise 2: Favoring minorities along racial lines is damaging to white people. ◦ Conclusion: Affirmative Action is reverse racism.

Application: Affirmative Action (Pro) ◦ Premise 1: Protecting minorities results in diversity. ◦ Premise 2: If America is diverse, American society will prosper. ◦ Premise 3: Affirmative Action protects minorities. ◦ Conclusion: Affirmative action will make American society prosper.