Introduction to Inductive and

Deductive ReasoningEnglish 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 ExampleEvidence: 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 SyllogismSyllogism: An argument arranged in three

parts1. Major Premise: General Principle2. Minor Premise: Specific Instance3. 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?

EnthymemeAn 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 PremiseShe 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

Recreate the Syllogism

Alcoholic beverages destroy brain cells, so alcohol should be made illegal.

You are all good students because you have your homework done on time.