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# Introduction to inductive and deductive reasoning

## on Oct 13, 2010

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## Introduction to inductive and deductive reasoningPresentation Transcript

• Introduction to Inductive and Deductive Reasoning English 1A Renee Bangerter
• Inductive Reasoning
• Specific General
• Inductive Reasoning
• Induction reasons from evidence about some members of a class in order to form a conclusion about all members of a class.
• A conclusion derived through inductive reasoning is called a hypothesis and is always less certain than the evidence itself. In other words, the conclusion is probable .
• Inductive Reasoning
• Induction can be done through the following:
• Observation
• Number Sampling
• Analogical Reasoning
• Pattern Recognition
• Causal Reasoning
• Statistical Reasoning
• Inductive Reasoning
• Inductive reasoning is used when examining all data would be an impossible task. In this case, induction uses statistical samplings.
• Inductive Example
• Evidence: Samantha took Renee Bangerter’s English 1A and got an A.
• Evidence: John took her English 1A and got an A.
• Evidence: I also know that Mike took her 1A class and got an A.
• Conclusion: If I take Renee Bangerter’s English 1A, I’ll get an A, too.
• You Try… “ Now let’s see—one sashweight, one butcher’s cleaver, on galvanized-iron tub, fifty feet of half-inch rope, one gunny sack, one electric torch, one pickaxe, one shovel, twenty pounds of quicklime, a box of cigars, and a beach chair.” Drawing by Chas. Addams The New Yorker Magazine From the Critical Eye by Sally Taylor, 1990
• Deductive Reasoning
• General Specific
• Deductive Syllogism
• Syllogism: An argument arranged in three parts
• Major Premise: General Principle
• Minor Premise: Specific Instance
• Conclusion: Follows Logically
• Standard, everyday language is arranged into verbal equations
• Syllogisms
• Major Premise : All men are mortal (general principle)
• Minor Premise : Socrates is man (specific instance)
• Conclusion : Socrates is mortal (follows logically from the major)
• Valid Argument: The conclusion follows logically from the major and minor premise.
• Practice with Syllogisms
• Major Premise: Stealing is a criminal act.
• Minor Premise: Shoplifting is stealing.
• Conclusion: Therefore?
• Shoplifting is a criminal act.
• Notice: A claim of definition
• is a form of syllogism.
• Valid and Invalid Syllogisms
• Major Premise: When Gabriele drinks coffee she always gets a headache. (Fact?)
• Minor Premise: Gabriele is drinking coffee.
• (Fact?)
• Conclusion: Gabriele will get a headache.
• Valid or invalid?
• Valid and Invalid Syllogisms
• Major Premise: When Gabriele drinks coffee she always gets a headache.
• Minor Premise: Gabriele has a headache.
• (Fact?)
• Conclusion: Therefore?
• Gabriele drank coffee.
• Valid or Invalid?
• True?
• Valid versus True
• Valid: the conclusion follows logically from the major and minor premise.
• Keep in mind—While we use the term “valid” in everyday speech, it has a very specific meaning in logic.
• True: Corresponds to reality, believable, provable.
• Sound: both valid and true.
• What Do You Think?
• Major Premise: Drug dealers wear electronic pagers.
• Minor Premise: Doctors wear electronic pagers.
• Conclusion: Therefore?
• Therefore Doctors are drug dealers.
• Valid or Invalid? True? Sound?
• Logical Fallacy: Guilt by association.
• Complete the Syllogism
• All Italians are volatile.
• Jesse is Italian.
• Therefore:
• Jesse is volatile
• Valid?
• True?
• Sound?
• This syllogism is based on a hasty generalization. Therefore, it is not sound.
• Complete the Syllogism
• All kids who wear Abercrombie and Fitch to school will be accepted by the popular group.
• Adrienne wears Abercrombie and Fitch to school.
• Therefore?
• She will be accepted by the school’s popular group.
• Valid?
• True?
• Sound?
• Enthymeme
• An argument in which the major premise is left unstated
• (often a conclusion supported by a single premise ).
• She must be a good student since she is on the Dean’s List.
• Conclusion Minor Premise
• She must be a good student since she is on the Dean’s List.
• Major Premise?
• All good students are on the Dean’s List.
• Examples of Enthymemes
• Alcoholic beverages destroy brain cells, so alcohol should be made illegal.
• You are all good students because you have your homework done on time.
Recreate the Syllogism